R.R.
Take him to court and if he is to pay 47% of child care and isn't I am sure the judge would be happy to make it easy for him to do and garnish his wages.
And, my understanding (at least here in CA) is that you can revisit the child support issue and if an increase is warranted it will increase, even if his paycheck is "gone by Sunday" or the fact that he has another child. (My neighbor has two older children from his first marriage, and three with his second. His current wife had to get a job because so much is taken out of his check for the older kids there wasn't enough to cover their expenses, he wasn't paying after he and she had their 3rd child and his first wife took him to court to garnish his wages. Pretty much the judge was "Too bad, so sad, get another job.")
Your ex has a financial responsibility to your son for 12 more years, whether it's hard on him or not.