We went to a wedding recently where there was a photo booth. One set of prints went home with the guest, one set went into a book for the bride and groom.
Arm the children with disposable cameras and a photo scavenger hunt list. Keep them entertained and get some cute shots of the wedding from their perspective.
Another Wedding photo idea I'm copycatting. Love how the pic is taken from behind and the "I Do" is just too perfect.