What age did you stop locking upstairs windows? Mine are 10 and 8 and I still lock them, especially as their bedrooms are on the top floor of our 3 storey house, but as it was so warm today I unlocked them all and had the windows open while they were at school and it would be so nice to be able to open them while they are here. The windows are high enough that you would have to climb onto something to fall out, and there is no furniture in front of them.