A person generally commits the criminal offense of sexual assault of a child—regardless of whether the person knows the age of the child at the time of the offense—if the person (1) causes the penetration of the anus or sexual organ of a child by any means; (2) causes the penetration of the mouth of a child by the sexual organ of the person; (3) causes the sexual organ of the child to contact or penetrate the mouth, anus, or sexual organ of the person or another person; (4) causes the anus of a child to contact the mouth, anus, or sexual organ of the person or another person; or (5) causes the mouth of a child to contact the anus or sexual organ of the person or another person.

The naming and definition of the criminal offense of sexual assault of a child varies from state to state. These criminal offenses are generally located in a state’s statutes—often in the penal or criminal code.

In Massachusetts, the criminal offense of sexual assault of a child is addressed under various statutes concerning sexual offenses involving minors. The state's laws define a range of sexual assault crimes, including rape of a child, indecent assault and battery on a child under 14, and aggravated rape of a child. These laws make it illegal to engage in sexual acts with children below a certain age, which includes any contact between the mouth, genitals, or anus of an adult and a child, as well as penetration of a child's body. The Commonwealth does not require the perpetrator to have knowledge of the child's age to be charged with the offense. The severity of the charges and the associated penalties can vary based on factors such as the age of the child, the age difference between the offender and the child, and the use of force or coercion. Convictions for these crimes carry severe penalties, including lengthy prison sentences and registration as a sex offender.