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 Missouri, the criminal offense of sexual assault of a child is addressed under the state's statutes concerning sexual offenses. Missouri law defines various degrees of sexual offenses that involve a child, including statutory rape and statutory sodomy, which can encompass the actions described in the topic. These offenses are considered felonies and are taken very seriously. The law does not require the perpetrator to have knowledge of the child's age to be charged with the offense. Statutory rape in the first degree, for example, involves sexual intercourse with a person who is less than 14 years old, while statutory sodomy in the first degree includes any act of sexual penetration with a person less than 14 years of age. The specific charges and penalties can vary based on the circumstances of the offense, including the age of the child and the nature of the act. Convictions for these crimes can result in significant prison time and mandatory registration as a sex offender.