Stuffed Animal Size Idea
Take a picture of your child with an enormous stuffed animal (e.g., Winnie the Pooh) every month of the first year. You can really get a sense of how they are growing. Frame them at the end of the year—they look adorable as a series! you can really see her growing. Also consider a once a year photo with the animal after the first year.
Newspaper (from Parents magazine)
Photograph your child holding the front page of the newspaper when significant events happen. That way when your child learns about that time in history, he/she will have a sense of how he/she fit into it at the time. If you scrapbook, you can then expand a little upon the picture about the personal impact of the event.
Penny Size Idea
Take a picture of your child with a penny on his/her hand when they are born, and throughout the years to get an idea of how they grow (I've also heard this done with a woman's bathing suit)
For your child's Birthday, write down things that you remember about the prior year (things they did, people that were special in his/her life, changes they went through). Do this letter EVERY year, and give it to the child on their 18th/21st birthday. (I really like this one!)
--- Instead of keeping Artwork or school projects, take a picture of it or scan it for their scrapbook.
--- The ABC book related to their life at the time (T is for Tea Lounge, N is for Naidres, P is for PowerPlay)
--- Put together a memory Time Capsule (sealed shoebox) with ticket stubs, favorite candy wrapper, TV show clipping, etc.)
---Take a picture of your kids outside of each of the house/building they live in as well as the building (I moved every 2 years until I was 16 and only have pictures of 2 of the 8 houses)