We have three APs in our house - my wife and I, and our 4 year old daughter. We got two books this week (on the same day) - one for my wife, and one for me. My 4 year old didn't get one. (I promise, we are sharing!)
The passes my wife and I have expire this week. My 4 year is on her second pass, and we just renewed it a couple of weeks ago.
Don't know if that makes a difference, just thought it was interesting.