Our DS1 (3.5) sleeps in a loft room, with lovely blackout blinds on the velux windows. It's really really dark up there, and he sleeps well.
But in this heat, it's sometimes 30C up there when he goes to bed. It doesn't seem to be bugging him, but it can't be good for him, surely? There are vents on the windows, so he's not suffocating, and he gets two sippycups of water in his bed, so he can drink all night, because of the sweating. He's not complaining, but it seems wrong ...
The other night, I went up after he was asleep, and opened one window a bit, and also left the hatch open. At 4am, he was downstairs, ready to start the day. He did not go back to sleep. So I can't do that.
We're having the builders in next spring, and I think I'll get a bathroom-style exhaust fan installed, and then I can leave it running at night. We might even get a radiator put up there, as it was often 10C up there in the winter, again it didn't seem to bug him.
My current solution is to leave the windows open during the day, and also go up after he's asleep, open a window and the hatch, and then go up later, before I go to bed, to close them both. Not great, but what else can I do?