Find something that your subjects like to do, then gather lots of photos of them in action and put it all together on a page. It's ok if the photos are from different years, I think that makes it even more fun.
My sons love water, I mean, really love it! I went through old photos and found many examples of them playing with water to create this page. To add to the water theme, if you look closely, you can see how I cut some circles out of the photos and popped them out. I was aiming for a "bubble" look with that, and it echoed the other circle elements.