I love taking photos, especially of kids. The problem is, they may not love having their photo taken. SO, here's what you need to do to change that...
Make them feel like having their photo taken is not a chore.
Have fun, act goofy and make them laugh! Don't be afraid to stand on one foot (only if you can balance well...) hop up and down or make silly faces. And definitely don't force them to do something that doesn't feel natural to them, it'll definitely show not only on their face, but through their body language.
I had the pleasure of shooting Mr. B one cloudy morning, and although he was a great smiler, his smile looked a bit forced. Plus, he kept looking at his mom standing next to me. What did I do? I took out my cell phone from my pocket and balanced it on my head, lens...well, you get the picture. I made funny faces and acted like a complete goofball, and it paid off!