Toddler climbing on windowsill - please help!

[LocalEditorOxford]

My two year old keeps climbing up on his windowsill so now we have to keep his windows latched on the 'child-safe' setting, about an inch open. The problem is the Airing cupboard is in his room and in the summer it's often creeping up towards 30 degrees with the windows shut like that - he's waking up in a muck sweat.

Whilst, in an ideal world, we'd be able to stop him from climbing on the [insert rude word] windowsill in the first place, that's just not going to happen any time soon, so we're thinking some kind of bars or something across his window.

If it makes any difference he has a deep windowsill (ideal for standing/squatting/jumping on) and a double glazed casement, much like this:

How is he getting on to the windowsill? (I'm on mobile so can't see you picture)

Is he likely to wake in the night and start climbing? Could you open it after he goes to sleep? Could you alter the timer on your hot water so it's not hot in the evening?

Depends on when he's getting there? Is he still in a cot/ contained at night? My dd can climb on our living room window sill now she's mastered climbing up the sofa- so we keep those on the saftey lock in the day then throw them open when she's in bed..... Can you do the same?