Caught Son Playing Doctor with Cousin

My stepson (12 years old) which I know since he was 5, was caught by my mom with my 10 year old niece playing doctor. We spoke to him and he said it was the first time and nothing happened. Concerned I asked my 6 year old daughter if he had done anything like that with her brother and she said yes. She cried and said that he had exposed himself to her and had asked her to show her self to him. I think he asked her to touch him and touched her, she did not want to talk about it anymore so I did not pressure her.
Even though I had explained over and over to her since she was 3 about her body, to say no and tell an adult. She said that she did not know what do do and did not want to tell me because she did not want her brother to get in trouble or for me to be mad at her.

I am very angry, I don't know what to do. I am concerned because I want to protect my baby girl. What should I do? He is way to old for this behavior to be normal right? was he molested and that's why he is doing this? do I take him to a therapist?

My daughter seems like it does not bother her, but I think it did and it does. I don't know if I should take both to a therapist and see what we can do to help both of them. But I am affraid that this will open up legal problems we cannot handle. Will he be arrested or charged with something?

I think I should just move out and take her and my other baby with me.
Please help

[Kevin Kennedy, Ph.D.]

Try to maintain your composure and do not take any rash action. Yes, it would be prudent for each of the children to be evaluated. At your son's age, 'playing doctor' is hardly an apt term for what occurred. Such inappropriate sexual behavior is not at all within normal bounds. Could it be that your son w3as exposed to some form of mistreatment himself? Yes, it is possible but not at all certain. Go ahead and arrange the evaluations.