At 4yrs old I would think you need to forgo the pull ups. They are old enough to have bladder control. They just haven't had a reason to control it yet. It's been 4yrs of soiling themselves...they can't be expected to train with a diaper on (a pull up is a diaper).

I don't know what to suggest. It's either on you to train this child (sounds like it could take a long while) or to just not take the initiative and leave it to the parents to do...but then you have to change a 4yrs olds diaper and I really don't know that that would be enjoyable. I think there is a point in age where the toddler cuteness factor fades and the whole diaper change is no longer do-able!! lol

Do you have a shower in your daycare bathroom? Maybe every time the child poops he has to undress himself and get in the shower to clean off? It seems mean i know but it might be enough incentive to have the child CHOSE to not poop himself at age 4. Of course, if there is a medical or developmental reason for the diaper this would just be cruel.

I would also INSIST the child comes in only jogging type pants. NO zippers, no buttons no buckles nothing to prevent a 4 yr old from pulling his own pants up and down. After the toileting is mastered then teach all those skills as well.