They are frozen in time with APs as well. My son turned 3 during the year but stayed 2 in Disney's eyes until the pass expired.
Sadly, if only I could have managed that in real life. I like my teen boy but would have liked to have kept him little a few more years.
Edited to add: ooops, not sure about the under 3 thing. I was thinking about back when they had child APs for ages 3-9. He turned 10 during the pass but stayed a child.