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 Utah, the criminal offense of sexual assault of a child is addressed under the state's sexual offenses statutes, specifically in the Utah Code. The offenses that involve sexual activity with a child are classified under different categories such as 'rape of a child', 'object rape of a child', 'sodomy on a child', 'sexual abuse of a child', 'aggravated sexual abuse of a child', and others, depending on the nature of the act. These crimes are considered serious felonies and the state does not require the perpetrator to have knowledge of the child's age to be charged. The statutes define a child as an individual under the age of 14 for certain offenses, and under the age of 18 for others. The penalties for these offenses are severe and can include significant prison time, potentially including life sentences for certain acts, as well as registration as a sex offender. It's important to note that consent is not a defense to these charges when the victim is below the age of consent, and the state takes these crimes very seriously, with a strong emphasis on protecting minors from sexual abuse and exploitation.