
They are probably getting most of their liquid requirements either from mum or because the food is soaked. But it would be good if you can work out a way of fixing the bowl onto the cage, as water should be offered too.
I don't want to alarm you, but my girl cleaned up after her puppy until she was about 8 months old or more!!! It was a major performance, praising puppy for pooing in the garden while also trying to casually snatch it up before mum ate it!! She did stop eventually though. :-D