Getting pills to "mellow him out" from "someone" and spending that much money on them sounds illegal.
Whatever he says, to you or to whoever you'll talk to - go by his actions, not by his words. As for what comes next in the short term: what do you want to do? You sound fearful for your and your children's safety. If you are, then trust your instincts and go to your parents.
he said if I want him to check himself in that he would go.
Check himself into what? A drug rehab program, a detox? If that's what he means then he's saying he has a drug problem.
Sorry this is happening. Safety first, then deal with your husband. Maybe he's telling the truth and this is the wake up call he needs. You will know it from his actions.