What most naturally follows?

How to babyproof windows
Lock your windows.
Many windows have built-in locks you can latch shut with a key to prevent the window from opening. If your windows have keys built-in, this is your best option for baby proofing your windows.
If your windows do not have keys, however, use another method. Installing keys is costly and time-consuming and it's far easier to use an alternative window locking method.