Hi Ladies,
We didn't have the exact problem, we had a diaper digger...especially during nap time or night time. To fix that problem I put her in pants and then put a one-piece, button at the crotch, outfit on her to keep her out of her diaper, which worked.
If the toddlers are going poo in their diapers I heard a trick that I haven't used but thought it was brilliant. The mom knew the child only would do a poo in their diaper so she cut a hole in the diaper and put them on the potty. If you know it happens about the same time each night perhaps that is worth trying.
Good luck and God Bless! I would love to hear if you try the hole in the diaper thing.
Sarah