Legally, he has to pay child support: whether he is self-employed or not has nothing to do with his obligations to his children.But there is a practical problem. When someone fails to pay child support, the usual remedy is to have his employer garnish his wages. (That is, send you a part of each paycheck.) But he is his own employer. He keeps the records about earnings; he is the one who would have to take some of his own earnings each week and send them to you. It is difficult to make a self-employed person fairly report and garnish his own wages. Not impossible, but certainly more difficult: if he refuses to pay, you can expect delays, difficulties, and costs (e.g. if you hire a lawyer to help you) to enforce your rights and get your children's money.