If your son is already in your custody and the custody of the child is not claimed by your wife he will remain in your custody.
Increase the custody of the child is fought by the wife then you have all the right to contest that the the boy is getting better situation and maintenance including upbringing with you.
She have only one plus. That the boy is below 5 years of the age so it can be be in the custody of mother.
Please remember to rate the reply if you liked it.