He may well be this protective over them now, but do the children ever see him take them? They may not realise how dangerous they are when they see their daddy popping them like sweeties.
It only takes once, one time he leaves a bottle or packet out, one time he's asleep and the kids go looking, and disaster. Maybe they only take one, hate the taste and leave it at that. But at their age/size, one could be all it takes to cause irreparable damage, or worse.
Even if they aren't at risk from him for being able to access the drugs, they're at risk of him not caring for them adequately. Drug addicts are not in their right mind, they often don't see dangers that are obvious to those not under the influence. This man should absolutely not be driving or have anyone in his care, he's not aware enough to prevent danger. And what if one of the children brings up seeing daddy taking all this medication? Is he as likely to fly off the handle repeatedly screaming at them the way you say he does with you?
Even if it all works out ok, and he manages his addiction, it will leave a lasting impression on your children. You have no idea how much of this they are picking up on and taking in. What if one day, they realise exactly what was going on, that you didn't put them first or protect them, and they end up hating you for it? Is risking losing your children, either by going to prison, having them taken away from you, or them hating you all by themselves for not removing them from this situation, worth protecting him for?