I would tell mom he needs to come more..... I don't do part time unless its for an already established family .... Currently I have one part time but they were full time but mom is on mat leave now and I will be getting the sibling in the fall. So I would tell mom that in order to make it easier on the child he needs to come at least four days a week till he adjusts and then gradually take away the days and see how it goes but if he reverts back then I would ask them to find other care.