I'm with Sassygirl on the fingerpainting - I take it one further and do not do crafts with anyone that is not capable of sitting at the play table. In other words for babies sitting in chairs other than a book to play with while waiting they get nothing but food on their trays as it is hard to teach them to distinguish between put this in your mouth, don't put that in your mouth, etc.

I would take advantage of the big kids being busy to set up a confined space for the babies to explore age appropriate toys without having to worry about being stepped on by the big kids but the space needs to be confined such that you can concentrate on the older kids.