DS18mo wears a long sleeve vest, pyjamas and a 2.5 tog grobag. He won't keep a blanket on. His room is usually around 19-21C at night.
DH likes to keep the central heating on all night because he worries that DS gets cold. Pre-kids we never had the heating on overnight and were never ill. Nowadays DH has always got a cold and I'm just getting over a sickness bug.
I don't believe it's healthy to have the central heating on all night but I don't want DS, who is not a good sleeper, to wake up cold.
What temp is your DC's bedroom? And what do they wear in bed?