Maybe this has been done before but I thought it would be lovely to collect ways of making memories of or for your children. Some parents make hand/footprints or moulds but there are heaps of things you can do as they grow.
These are my ideas - they are all to do with photos but I'm sure others will have different ideas:
Take a photo of your newborn child next to a large stuffed toy. Then continue to take a picture with the same toy every birthday.
Take a photo on the same day of the month (birthdate probably easiest to remember) everymonth_ for the first year. On your child's first birthday you will have a record in photos of their first year. If you find a frame with 12 small spaces you can display them.
Take a photo every birthday of your child wearing an item of clothing of yours or your dp that you no longer wear. A girl might wear an old dress and a boy an old shirt or t-shirt. It will be huge of course at first but it is wonderful to see how they grow into it! It can become part of birthday tradition to pose for the photo!
Oh last thought - keep a height chart! It is such a small thing but we all love looking at how dd and ds have grown over the years. Great to see when the growth spurts happen too! (You know you weren't imagining it - and why the food bill went up!)