For my mum's 60th, I got all our childhood photos and picked about 20 that were right for the task. Then, my sisters and brother and I spent one mad day recreating them all. We dressed up, used props, went to the places where the originals were taken or just found somewhere that looked the same, lined up the shot while looking at the old one and took it again! We borrowed a school tie to take one of my brother (36) to make him look 6 again, made a plate of play food to look like the first Sunday lunch my sister made, and posed in the kitchen with at 11 - then made her pose again with the pretend one etc etc...
We had so much fun, and I made up an album, with each photo next to its modern version. Mum looked at the first few pages and said something like "how nice" obviously thinking we'd just made her any old photo album. I closed it up and told her to start again, and to LOOK at it. When she 'got' it at last, she cried and cried and cried. She was totally speechless! It was the BEST idea I have ever had, and she still goes on about it now - 10 years later!!
Hope that helps?? Happy birthday from me! xx