The idea was to get them to realise how history is collected. You ask them to remember as far back as they can, and then you go back farther for them in YOUR memory and you recreate their entire personal history. Because, of course, they don't remember being born, but it is kind of important that that would be on their personal timeline. You know? So you get to share that story with them and others from before they remember, and then slowly, you get up to the dates they remember, and you start adding those in too. For my kids, after we got to things they remembered, they took off, telling me everything that they can about the time I am talking about in our lives.
You can distinctly see the time when we didn't have a camera in Alex's timeline. From ages 3 to 6. lol... there are lots of blank spots. My camera got stolen and we could not afford to get another one until 2005.