My husband is mentally handicapped and I do NOT want him to any kind of custody of our son. I do not trust him to be alone with our son. Worst I do not want my son with his (husband) parents alone, I do not approve of their kind of discipline

Whether you approve of their discipline or not, he is the father and he does have rights to the child.

How is your husband "mentally handicapped?" Is he depressed? Mentally retarded?

Mentally retarded
For discipline I don't want them hitting my child

Then in court at the child visit hearings you will need to prove the father is a danger to the children and can not visit without supervision. You will need court accepted evidence.

If you want his parents restricted, you will have to prove they have a history of child abuse and that they would hit the child.

My husband is mentally handicapped and I do NOT want him to any kind of custody of our son. I do not trust him to be alone with our son. ...

Then why did you marry, and have a child with, the man?

Do you do realize that until modified by a court order, he does presently have full custody rights (the same as you have) with respect to his son?

Not abuse just spanking
I thought people could not even spank other peoples kids

Not abuse just spanking
I thought people could not even spank other peoples kids

Spanking is still an acceptable form of discipline. It just depends on what level it is going to that can make it abuse.