Take pictures of a favorite toy while travelling
Kirsten has a great suggestion for making vacation photos more interesting for kids:
Send one of your kids' small toys with people you know who are travelling. Kinda like the 'flat stanley' idea. The travelers take pictures of the toy on their trip (with landmarks and other interesting backgrounds) - which makes the pictures more personal for your kids. We have a cat (Meemo) who has been all over the world in the last 3 years - I just blogged about it - with more info, tips, and pictures.
My cousins did something similar on a recent trip. Their children took pictures all over with "Flat Montana" (Montana is their beloved cousin who was still at home), and then Montana's mom had all the photos printed in a Shutterfly photo book. The result was gorgeous.