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 Montana, the criminal offense of sexual assault of a child is addressed under the state's sexual assault laws, which are part of the Montana Code Annotated (MCA). According to Montana law, a person commits the offense of sexual assault if the person knowingly subjects another person to any sexual contact without that person's consent. 'Sexual contact' is defined to include any touching of the sexual or other intimate parts of the person for the purpose of arousing or gratifying the sexual desire of either party. When the victim is a child, the offense becomes more severe and is often referred to as 'sexual intercourse without consent' or 'sexual abuse of children.' The law does not require the perpetrator to know the age of the child, and certain acts, such as those described in the provided topic, would fall under these statutes. The penalties for sexual assault of a child in Montana are severe and can include significant prison time, with harsher sentences for offenses involving younger children or for repeat offenders.