How can I get my ex who recieves ssi to pay child support?

My ex got me pregnant twice now and has received SSI since he was very young. We are no longer together and he does not help me take care of them financially at all and I feel that he can help me take care of his kids. We already had a child support hearing and because he recieves ssi and not ssdi he dont gotta pay nothing! He gets more money then me financially right now and there his responsibility too. Futhermore my tax dollars are going to his lazy ***! It infuriates me!! I'm helping give him money and he dont got to give his kids anything! Is there anyway possible I can change this???? How can him and like him be able to get away with this!?! Make kids and not have to help take care of them financially and sit on their es all day and use all there money on drugs and alcohol! While me and his kids are struggling. It sickens the *** out of me! Please somebody let me know if there is something that can be done. Thank you.