Sexual abuse is one form of child abuse. It includes a wide range of actions between a child and an adult or older child. Often these involve body contact, but not always. Exposing one's genitals to children or pressuring them for sex is sexual abuse. Using a child for pornography is also sexual abuse.
Most sexual abusers know the child they abuse. They may be family friends, neighbors or babysitters. About one-third of abusers are related to the child. Most abusers are men. If you think a child may have been abused, it's important to report it.
References and abstracts from MEDLINE/PubMed (National Library of Medicine)