Ok maybe that's a little drastic but really not saying cheese has it's benefits. Let's look at it.
Food for thought:
How often have you had your children say cheese only to get some ridiculous monster face? You know they just can't resist right? It is funny but doesn't always make for the portrait you are looking for.
I find that children are much more likely to give you the kind of smiles that you want by having a simple conversation with them about their most favorite activity in the world. Such as their favorite day at the park. I also find that they are just beyond happy to share their most precious lovie in the world. Whether that be a blanket or a stuffed animal. It makes for some very adorable pictures as they cuddle their most prized possession in the world.
I love smiles too but what really makes my heart go pitter patter is a picture that seems to pier into the subjects soul.