Hey there, Mike. Welcome aboard.
A recurring complaint over the years has been "what do we do about those campers who slam their doors?" This is a good opportunity to talk to your kids about the impact they have on other campers.
As far as closing the door more quietly, we usually operate the latch handle while we're closing it. Grab the latch and hold it open, hold it by the latch as you're shutting the door, and then tug it firmly to make the latch shut itself.
Other than that, take a look at the orientation of the door latch and the strike plate and make sure they're lined up OK. If not, loosen up the strike plate and move it into a better alignment.
Hope that helps. And have fun with the kiddos.