A child rarely lies about being molested. They are probably already dealing with guilt feelings, especially if the offender is a relative or close family friend. Do not blame the child for what happened. Cooperation is not he same as consent. A child doesn't have the mental capacity to consent to sexual interactions.
Fear can keep a child from telling someone for a long time.
Keep the lines of communication open. Encourage your children to ask questions and talk about problems. Sometimes, good touches, like hugs, can feel bad. Some adults don't know they shouldn't touch children on their private parts. Adults that touch children on their private parts need help.