wrote:

It's about 5 degrees colder I think though I never measured it. The
younger one (3yo) doesn't like blankets. The older one (4yo) uses a
blanket but doesn't know how to re-cover herself if the blanket shifts
during the night. She's a light sleeper so gets irritated if the
blanket doesn't stay in place. So on colder nights they end up in my
bed for warmth. Given your list of cautions, I think a room heater may
not be a good idea. It's a carpeted room with curtains and beds on the
floor. Adults won't be present when the heater is working.

Anyone has any other suggestions?

Warmer pajamas. With kids that young, I wouldn't get
a wink of sleep with a heater in their rooms. Just put them
in however many layers of clothing they need (pjs with footies! ;-) )
to stay warm at night.

Best wishes.
Ericka