When we were expecting Thomas, we received great advice from our Executive Director at work. He suggested we get journals and write to our little one(s) each month.
Mike had heard about this at a recent couple's baby shower he and his wife attended and wished he had been writing to his sons all along. I headed to Barnes & Noble that afternoon and picked up a blank journal. The next day we had our ultrasound and found out we were having a boy! I started journaling to Thomas that day. And have been for 9 years this month.
With Brennan, I started journaling right after he was born. The boys sometimes ask for me to read excerpts from their journals to them at night. I'm on their 3rd journals now. Their birthday month I ask them about their favorite things (foods, tv shows, books, movies, friends, classes...) and they help me with that entry. I haven't turned the journals over to them yet - I will wait until they are much older and maybe have responsible wives who will put them somewhere for safekeeping!
I try to write a few pages every month and am pretty good about it. There have been times where I've skipped a few months and I miss so much! I love going back and re-reading old entries.
David also has journals for the boys with this own approach. I hope the boys appreciate the tales from their childhood when they have their own little ones at home.