is it legal for my sons mother to deny me contact with my child

There is not NEARLY enough information provided to hazard any response to that question beyond "maybe." Are you on the birth certificate?  If not, have you been adjudicated the father of this child?  Are you or have you been married to the mother?  Did you ever cohabit with the mother?  How old is the child?  Where does everyone live?  How long have they been there? I suggest you look over the child custody and (if applicable) paternity pages of our website, which may answer your questions.  If not, consider asking a more detailed question or (better) scheduling a consultation with a family law specialist to go over your particular facts and circumstances.