Yes, possibly foundered (or laminitis episode, if you prefer) or his feet were neglected at some point in the past and they are still are a work in progress. If he was foundered, he could well be sound enough for your children to use with the codicil that his diet must be watched closely to keep his weight under control (over weight being the likely cause of founder in the first place, if it happened). If it was neglected feet, then it's a case of letting the process continue to return the feet to proper shape. It's hard to tell from the picture but I would speculate he can move around just fine.
So, under these circumstances, it would probably be a good idea to do a pre purchase exam or at the very least speak with the vet who treated him (if that's possible) if the owners acknowledge he foundered in the past.
Best of luck with it and I hope it works out for you as he's a smart looking little chap.