Fun Ideas
Get a book and have your kids classmates sign it every year. I used the Dr. Suess book Oh The Places You'll Go. near the end of the school year I email the teacher and ask if I can send it to school to have the whole class sign it. Remember to have the teacher sign it also. Once they got out of elementary I had their friends sign it at their birthday party. Great to give them at high school graduation.
Every year at my husbands birthday I have the girls put their hand print in a hard covered book with paint and write a little note next to it. It is fun to look back when they were toddlers and just scribble and compare it to the nice messages as they got older. Remember to date each one.
Sign up for an email when your kids are young and over the years send them emails and when they are older give them the email to access them all. You can send notes of encouragement, advice, photos, and jokes.
Each year of your child's life put memorabilia in an envelope from the year and at the end of the year write a letter to your child about the past year and seal it. Give them all the envelopes when they graduate from high school. You can put things from school, newspaper clippings, photos, and anything you can think of that reminds them of that year and what happened.
Take a picture of your child in front of their school the first and last day of school every year and when they graduate you can put them all together on a poster board to see how they grew and changed over the years.