My wife and I have a littler of pups. In the beginning the mother cleaned up after them but are starting to get weaned and she does not do this any longer. What can we do?

My dog recently had a litter of pups which are all doing great. My only problem now is that they are turning 4 weeks old this Thursday and we have began weaning and an attempt at house breaking. Up to 3 weeks old they mostly urinated in their whelping box and the dam cleaned up the mess fairly quickly without us noticing. Now that they are teething, getting rougher with the dam and eating puppy mush she has been leaving them to themselves for longer periods. Unfortunately for my wife and I, when we get home or wake up in the morning, their blanket is usually soiled with urine and/or feces. Our normal routine is to take them outside, (if its not cold, which it has been for the last week or so), or put them on a much frowned upon dog pads after waking, eating and playing. To no surprise it's not working, some pups have been doing great with the pad making clean up a breeze while others either use the pad rarely or not at all. We even reduced the size of their whelping box to an approximately 2'x2'x4' plastic storage container. It seemed to work with feces but not urination but the dam was not able to get in with her pups which made them yell and eventually they figured out how to scale the walls to get out so we tossed that idea. Now they have taken over a closet where they use half for relief and half for rest, but again most aren't using the pad. Help what can we do? Is it to early to start house breaking?