In view of his behaviour, I don't think the idea of staying overnight should come into it.
Do the DGC like spending time with him? If not, why persevere with it? If they do, then daytime visits only would seem like the best way.
Some good suggestions from Eloethan.
Does anyone have a really simple diet plan?
Change the name in a tv show /movie title to the above user username
CONTINUATION of write a word beginning with the first letter of the name of the user above you
and 

None of us believe he would be violent with the children but I take all the points above.