Doesn't make sense to me....
Why wouldn't they leave sooner?
Seriously, I really don't get it.
Maybe easier said than done but its hard for me to believe they had a window, a key to the door that they made, and no supervision the majority of the time.
If they HAD been completely locked in with no window or ability to go down the roof, and then they got the key, I feel like they would have sprung free immediately.
Maybe I'm just more feisty but I would have gotten the F OUT OF THERE waaaaaaay sooner.
They could have stolen stuff a lot sooner and flown the coop. I might have just been a rebellious child but it's so hard to believe they'd stay for years with a working window.