One of the best ways to help a photo shoot, is to bribe the right way. During the years I worked for a national studio, I was surprised at how many parents threaten to take away toys if their kids won't smile. Maybe this works at home for some people, but it never works for pictures. In pictures you want children to be happy and while threatening to take away their favorite toy at home may get them to stay at the dinner table, it doesn't make them smile. I have seen parents go as far as actually throw a toy in the garbage can, trying to bribe smiles, and then been frustrated when all they ended up with was quivering lips and tears. This is the point in a session where I usually asked Mom to take a break and let me work with the kid alone for a few minutes. Mom would usually come back a few minutes later, surprised to see her child smiling and happy, with the fear of losing their favorite toy gone.
Now, owning my own photography business, I always carry around a few bribes in my camera bag. Not every photo shoot needs to end in candy, but a shoot will always go smoother if mom or the photographer are prepared.