You know the game... The one where you say "I'm going to get you!", slowly move towards the kid while wiggling your fingers and tickle them for a second, back up, then do it all over again. I will tickle the kids once, back up, focus, fake another attack, and take a few photos when they giggle. As a bonus, you get a great workout running around.

Peakaboo

Play peakaboo behind your camera. Make sure the camera is pre-focused and ready to capture the smile. This one works better with younger kids (up to about 2ish).

Another variant of this is to have someone hide behind the photographer, pop-out, hide again, pop-out… and you get the point.

“Daddy Smells”