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.
Ethical question - how do you feel about second chance??


and 

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