I think you were brave to post, and i am appalled at any breeder selling a dpup to someone with such young DC/babies.
Like other's say. its not fair on anyone. the poor dpup will be feeling its always in the wrong. You cannot possibly be caging the dpup, as thats not fair on it, nor can you have 'lines' in a house with toddlers.
No wonder you feel as you do, the reason being, it is too much, and all are at risk, not least you! from the sound of your post it is too much.
it takes one playful snap from dpup to rip open toes, ears, face of baby/toddler.
I can hear that you got the dpup with the best intentions, and again, it is down to a breeder to tell you that it is very ill-advised and to not sell you a dpup because of the very real risks involved to all,, and not only that, but to give advise on management (if DC are old enough). Dpups can be extremely hard work, but are very snappy /nippy and will find having young ones around extremely stimulating so whilst you are busy trying to ward it off dc's, noises and movement are further stimulating it to more snapping.
DCs, without intention, encourage dpups to high levels of excitement and are a risky combo, the younger they [both] are, then the more risky.
My head spins at how you can possibly manage all this safely and without detriment to any party. Its hardly the best start for any is it?
You have some good advice already, but most of it is how to keep them all apart?! ... and i wonder at the point of that.
Again, you have been brave to post for guidance, and you have only done this because you thought you could, and i'm sure others, many, have done the same, and many more will continue to, but i do despair at breeders selling dpups into these situations, because its far from teh best start for a dpup, not knowing what the stress will produce in the adult ddog who would then get blamed for any 'bad' behaviour. Poor dpup 
poor you and dc's.
and strength, and extra [wo]manpower to you. I think you need a lot more people around, or farm your dpup out to others during the day who can give it the time and training it needs without all the stress and hyper stimulation, just until this phase calms down and is under control.
I hope you can find some wiling volunteers - I'm sure you will!