Here's how it works. If he can't meet the obligations, the government will do so on his behalf (because we don't want children to starve) but it's not for free. He signs up for the next, say, 5 years. The government takes a portion of his pay for the family, perhaps with a bit of topping off.
Mom has to commit to no more children. If she does, she's cut off the dole and her boyfriend will have to carry the load.
Dad has to commit to keeping in touch with the family.
Why the army? Because it is an organization that tears down an individual's arrogance and builds him back up again with a sense of responsibility and maturity.
The also provide housing for soldiers. Moving these women out of their current neighbourhoods might be a good idea.
So these young dads lack a father figure? Say hi to your new dad. You can call him "Sarge". But whatever you do, don't call him "Sir" -- he ain't no officer, he works for a living. And when he tells you to drop and give him twenty, he's doing it because he cares.
Nice side effect is that mom now has to live with the knowledge that her boyfriend is in the army now. So much for lack of consequences. And if she forgets, I bet he's got family who will remind her.
When he leaves the army, I'm willing to bet we'd have a fine citizen on our hands.
I can think of a 100 reasons why this won't work, but it's better than what we're doing now.