One of the simple ways I document life is via Photobooth on my computer.
The kids love it. I get myself in the story.
Sometimes you have to take matters into your own hands (or click a button on your computer) to make sure you're visually included in the stories you're telling.
Wouldn't it be cool to have a set of shots like this of your Mom or Dad or Grandparent or other loved one from a certain point or over a span of time?