There is almost nothing as intriguing as your parents diaries. Not that I've ever sat down and read them, but sometimes my dad will pull out his laptop and read us clips from when we were little. There is so much fodder there for character and story, not to mention understanding of yourself.
Here is an example from Dad (shared with permission):
I just went downstairs to stop Rachel and Sarah from fighting. Sarah only has two barbies and she only wants Rachel to have two. I said she should let people do what they want and not be so bossy. I said, "you can only really play with two barbies at once, cause you can only hold two barbies at a time." So she picked up four barbies and played with them. Then I said, "but only 1 barbie at a time can talk." She said, "not if they all say the same thing."Um, yeah, so that's the kind of kid I was. The jury's still out on if I've improved. The point is, our parents remember things about us and all our siblings that we, obviously, don't, and there is not much I can think of that gives us more to work with then our own family and personal history.
If you're lucky enough to have parents that kept records, ask if they'd be willing to share some little bits with you.
What kind of a child were you? How has that informed your writing and authorial career?
P.S. I'm the one in the plaid jumper, Rachel's in the floral. We no longer fight over barbies. More than once a week.