I often tell people that doing what I do is just about being ready with the camera when the moments happen. You can rarely coax a kid to do That Perfect Thing, in order to get That Perfect Photo.
Most every session, though, I have a moment. Usually I'm not completely paying attention. I'm chatting away with a young client's mom, when I see something perfect. I usually approach the shot calmly and just let the child be themselves.
This shot developed that way. Girl 1 was being herself, Girl 2 saw that Girl 1 was having her photo taken and jumped in on the action, then Girl 3 came along and gave the pair of them a big squeeze. There is no way on earth I could have posed this shot.
Sometimes the best advice I can give to Moms who want to take great photos of their kids, is just have your camera ready when moments happen all on their own. Don't pick up the camera with big plans, pick it up with a willingness to observe and create. These moments can't be faked or re-staged, so be ready!