I like this as a way of displaying family pictures too! If you still wanted to do the traditional family tree, you could always use this idea for displaying pictures taken in the classroom and pictures with friends - their "classroom family"
pine needle discovery bottles - Make with the kids at preschool. Add water, pine needles, and glitter to a water bottle and hot glue cap on top. Use different evergreen, so the kids can see the difference. Kind of a 'I Spy' theme
When i have my own preschool center, this will be an indoor play space! Nest, 1301 Locust Street, Philadelphia awesome space for kids, wish their was something like this around my house (of-course when i have kids)