Plaintiff, Cara Lyn Landreth, by her guardian ad litem, appeals from a judgment dismissing her action against the United States under the Federal Tort Claims Act (FTCA), 28 U.S.C. §§ 1346 (b), 2671 et seq. We affirm.

*533 I. FACTS AND PROCEDURAL POSTURE

During the morning of March 30, 1973 Cara Lyn Landreth, who was then eleven months old, swallowed a portion of her mother’s quibron medication. Her mother, Jennie Landreth, and her father, William Terry Landreth, who was a member of the United States Air Force rushed her to the Plattsburgh Air Force Base Hospital. No physician examined Cara at the emergency room. Jennie Landreth heard a physician instruct an orderly to give Cara 15 cc. of ipecac and then send her home. The ipecac was administered and the Landreths returned home. That evening Jennie noticed Cara’s eyes had rolled back and she was convulsing. Cara was immediately taken back to the Plattsburgh hospital by her parents. She was then transferred to the Montreal Children’s Hospital where she remained hospitalized for six days. The medical personnel at the Montreal hospital told the Landreths that Cara’s seizures were due to the quibron ingestion and that her stomach should have been pumped at the Plattsburgh hospital when she was first taken there.

When Cara was fifteen months old, Jennie noticed she was easily angered and had temper tantrums. At eighteen months Jennie noticed Cara’s communication skills were retarded. A base doctor in the Philippines where William was stationed recommended that Cara be examined by a specialist.

In 1977 or 1978, Jennie took Cara to the UCLA Neuropsychiatric Institute where a doctor performed a brain scan on Cara and determined she had suffered brain damage as a result of the ingestion of quibron.

Prior to 1979 both William and Jennie Landreth frequently discussed their belief that the Air Force was responsible for Cara’s problems because the doctors failed to pump Cara’s stomach on the morning she consumed the quibron.

During 1979 Jennie told a doctor at the UCLA Neuropsychiatric ward that Cara's problems were partially attributable to her ingestion of quibron.

Plaintiff filed an administrative claim dated September 6, 1983 under the FTCA alleging the Air Force was negligent. The Air Force rejected the claim on May 15, 1984, finding the claim was time barred.

On November 7, 1984 a guardian ad li-tem was appointed for Cara and suit was filed in district court. The United States filed a motion to dismiss and for summary judgment. The district judge trifurcated the statute of limitation issue from the issues of liability and damages. After argument, the district court held the suit was barred by the two-year statute of limitations under the FTCA, 28 U.S.C. § 2401 (b) and dismissed the action.

Cara Landreth appeals, contending that (1) her parents did not know or have reason to know of the existence of facts establishing the government’s responsibility for her condition until a period within two years of the filing of her claim, or (2) the statute was tolled until a guardian ad litem, without a conflict of interest, was appointed to represent her.

II. DISCUSSION

Under 28 U.S.C. § 2401 (b), a tort claim against the United States must first be presented to the appropriate federal agency within two years after the claim accrues before a negligence suit may be instituted. Failure to do so is a jurisdictional defect. Augustine v. United States, 704 F.2d 1074, 1077 (9th Cir.1983). The date on which a claim accrues is determined by federal law. Washington v. United States, 769 F.2d 1436, 1438 (9th Cir.1985). In a medical malpractice case under the FTCA, a claim accrues when the plaintiff discovers, or in the exercise of reasonable diligence should have discovered, the injury and its cause. See United States v. Kubrick, 444 U.S. 111 , 100 S.Ct. 352 , 62 L.Ed.2d 259 (1979); Colleen v. United States, 843 F.2d 329, 331 (9th Cir.1988); Davis v. United States, 642 F.2d 328, 331 (9th Cir.1981). Plaintiff need not be aware that an actionable claim exists as long as she is aware of the injury and its probable cause. United States v. Kubrick, supra.

*534 The district court’s grant of summary judgment is reviewed de novo. Darring v. Kincheloe, 783 F.2d 874, 876 (9th Cir.1986). Review is governed by the same standard used by the district court under Fed.R.Civ. P. 56(c). Id. We must determine, viewing the evidence most favorable to plaintiff, whether there are any genuine issues of material fact and whether the district court correctly applied the relevant substantive law. Ashton v. Cory, 780 F.2d 816, 818 (9th Cir.1986).

Here any knowledge Cara’s parents had of Cara’s injuries and the cause of her injuries is imputed to her. Fernandez v. United States, 673 F.2d 269, 271 (9th Cir.1982). The fact of minority does not toll the statute. Brown v. United States, 353 F.2d 578, 579 (9th Cir.1965). Rather, the minor’s parents have a legal duty to take action on the child’s behalf. Washington v. United States, 769 F.2d at 1439 . The date the Landreths first discovered the existence and cause of Cara’s injuries is a question of fact reviewed under the clearly erroneous standard. Colleen v. United States, at 331. The date the Landreths should have discovered the existence and cause of Cara’s injuries in the exercise of reasonable diligence is a mixed question of fact and law and is also reviewed under the clearly erroneous standard. Id.

The district court found Cara’s parents knew or should have known of their daughter’s injury and its cause no later than 1979. The record supports this finding. Jennie Landreth informed Dr. Lillian Lessor at UCLA Neuropsychiatric Ward in 1979 that Cara had ingested quibron at the age of eleven months. Jennie also told Dr. Lessor she believed Cara’s behavioral problems were related to that incident. William Landreth testified that prior to 1979, he and Jennie discussed the failure of the physicians at Plattsburgh Air Force Base Hospital to have Cara’s stomach pumped. Dr. Gabriel of Century City, California performed a brain scan on Cara before 1979, and his diagnosis was that the quibron ingestion was a cause of her brain damage. Therefore the court concludes the district court’s finding that Cara Landreth, through her parents, was aware of the cause of her injuries and the responsibility of the medical personnel at the Plattsburgh Air Force Base Hospital for those injuries no later than 1979 was not clearly erroneous. We therefore affirm the district court’s ruling that Cara’s claim was not timely filed under the FTCA.

Nevertheless appellant argues that Jennie Landreth may have been partially responsible for Cara’s injuries because she did not place her quibron medication in a secure area. Therefore, appellant maintains both Jennie and William Landreth had a conflict of interest in pursuing this claim. Appellant contends the statute of limitations for filing the FTCA claim was tolled until a guardian without a conflict of interest was appointed for Cara. To hold otherwise appellant suggests would constitute a denial of due process and equal protection of the law.

Appellant relies on Washington v. United States, 769 F.2d 1436 (9th Cir.1985). That reliance is misplaced. In Washington an adult woman became comatose as a result of the alleged negligence of Air Force physicians. Eight months after her death her husband filed a FTCA claim. The court held that Washington’s claim did not accrue until her death because she was an adult and no one, including her husband, had a legal duty to bring an action on her behalf. Washington, 769 F.2d at 1439 . Here Cara’s parents had a clear duty to preserve their child’s claim by timely action as the Washington court observed when it distinguished Brown v. United States, 353 F.2d 578 (9th Cir.1965) and Fernandez v. United States, 673 F.2d 269 (9th Cir.1982) where the parents had a duty to commence legal action on their children’s behalf because they were minors. Washington, 769 F.2d at 1439 .

Nor can this court accept appellant’s contention that the alleged conflict with her mother denied her due process and equal protection of the laws. A similar argument was considered and rejected by this court. In Pittman v. United States, 341 F.2d 739 (9th Cir.1965) a father commenced an untimely FTCA action on behalf of his minor *535 child alleging the Navy negligently injured his son. The father alleged he waited to file the action because he feared that bringing such an action would jeopardize his naval career. The son argued this conflict should extend the limitations period. The Pittman court, in considering and rejecting this argument, said:

341 F.2d at 741-42 . The Pittman court also rejected the due process and equal protection claim, stating:

341 F.2d at 741 .

The FTCA is a limited waiver of sovereign immunity. The purpose of the two-year limitation provision of Section 2401(b) is to encourage the expeditious disposition of claims. As the Supreme Court stated in United States v. Kubrick:

Here more than ten years elapsed between the alleged negligent acts of the government and the filing of the administrative claim. It is precisely this type of delay the limitation provision of the FTCA was designed to guard against. While the court is not unsympathetic to Cara’s condition, principles of equity cannot be invoked to toll the accrual date of plaintiff’s injury for statute of limitations purposes. Washington v. United States, 769 F.2d at 1439 ; Burns v. United States, 764 F.2d 722, 724 (9th Cir.1985). Congress has clearly manifested its intent that there must be prompt disposition of FTCA claims. This court does not, as the Pittman court did not, find the plaintiff’s claims to be of constitutional proportion. Therefore it should be left to the Congress and not this court to provide for the tolling of the statute if policy considerations suggest that it should do so.

For the reasons set out above the court concludes that this action is barred under 28 U.S.C. § 2401 (b).

AFFIRMED.