There is a statute of limitations, but it varies from state to state. Also, in the case of child abuse, the statute of limitations can begin to toll when the child turned 18, as opposed to when the abuse occurred.
I can not answer for Washington, DC, but in California, the statute of limitations is as follows:
Special Childhood Sexual Abuse SOL : 26 years old (18 years old + 8 years).
Limited Discovery Rule : 3 years. Actions against a person for committing childhood sexual abuse may be brought “within 3 years of the date the plaintiff discovers or reasonably should have discovered that psychological injury or illness occurring after the age of majority was caused by the sexual abuse”.
Criminal Statute of Limitations
Delayed SOL for most sex crimes against victims less than 16 : Until victim is 28 years old. Allows prosecutions for a number of felony sex crimes (sodomy, oral copulation, and sexual penetration of victims less than 16, and performing lewd or lascivious acts against a child under the age of 14) committed against victims younger than 18 to be brought any time before the victim’s 28th birthday.
Reporting Window: 1 year : After the above SOL has expired, prosecutions for a sexual crime committed against a victim younger than 18 may be brought within 1 year of the date a report is filed with a state law enforcement agency. In this case, the allegations must be corroborated by some sort of hard evidence rather than the victim’s own testimony.