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 Michigan, the criminal offense of sexual assault of a child is addressed under the state's Criminal Sexual Conduct (CSC) statutes. Michigan law categorizes various forms of sexual assault into degrees, with First Degree Criminal Sexual Conduct (CSC 1) being the most serious. This includes sexual penetration with a person under 13 years of age, regardless of the assailant's knowledge of the child's age. The other actions described, involving contact without penetration, may fall under Second Degree Criminal Sexual Conduct (CSC 2) when involving a person under 13, or Third Degree Criminal Sexual Conduct (CSC 3) when involving a person between 13 and 16 under certain circumstances. Fourth Degree Criminal Sexual Conduct (CSC 4) involves certain types of touching. Michigan law imposes severe penalties for these offenses, including lengthy prison sentences and registration as a sex offender. The specific statutes detailing these offenses and their penalties can be found in the Michigan Penal Code, MCL 750.520b to MCL 750.520e.