I cought my 4 year old son touching my 6 year old daughter what shound I do

I feel that you should contact your medical insurance and have them refer you to a therapist for your son

Touching? How? What?

He's only 4. What does he know?

Why are you so worried?

This is completely normal for children of that age unless he is being abusive about it. The best thing you can do is to monitor it but not make a scene; he is at the stage where he is beginning to learn the physical difference between girls and boys. No biggy!