I can't afford health insurance for my children, what can I do?

I am a single mother with three children and I can't afford to put them on my company health insurance. Their dad is supposed to pay for their health insurance, but he usually forgets to send me the money and I have to pay it. He did not send the money for the last 3 months and I can't make the payment to the insurance company, so they are going to lose their coverage. What can I do?