You should file a case against your ex-husband, before the court of the first-class Magistrate under section 125 crpc for alimony (maintenance) of your child. He is bound to give maintenance at the age of 18 years. He cannot refuge it. It does not matter that you have remarried to any other person. Your child has the right to get a share in his father’s property. He has the right of inheritance in his father’s ancestral property. If his father refuses to maintain him, he can file such case under section 125 crpc.
At the stage of the decree in a divorce case, the court should decide permanent alimony for the minor child. Such maintenance is necessary for the education, social welfare and upbringing of the child. It is the absolute liability of his father to take care of his child up to the age of 18 years if the child is not suffering from any infirmity (Amar Somnay vs Prerna Sharma AIR 2016).
However, you have custody of the child, but you have no right to give him in adoption to any other person without the consent of your ex-husband. Permission of the father is necessary for adoption if the father is alive and able to give consent. Adoption without the consent of the father is void in law, and the court shall cancel it on the application of his father.