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 Idaho, the criminal offense of sexual assault of a child is addressed under the state's statutes concerning sexual abuse of a child under 16 years of age. According to Idaho Code § 18-1506, it is a felony for any person to commit any lewd or lascivious act upon or with the body or any part or member thereof of a child under the age of 16, with the intent of arousing, appealing to, or gratifying the lust, passions, or sexual desires of such person or of such child. This includes any of the acts described in the provided topic description, such as penetration or contact of sexual organs or anus, regardless of whether the perpetrator knows the age of the child. The law does not require that there be actual physical resistance by the child. Conviction for sexual abuse of a child can result in severe penalties, including imprisonment and mandatory registration as a sex offender.