I feel like I should know the answer to this already 
Years ago when DS was a toddler and we were moving from sleeping bags to duvets, I read some guidelines online which said that toddlers don't need a high Tog duvet. So I got him a 4.5 Tog one. Now he's almost 7 and still using the same duvet all year round! His room is usually warm as it gets the sun for most of the day, and that could be why he's never complained of being cold.
I was just wondering if you get different togs for your kids for summer and winter?
Also 2.5 year old DS2 should now be moving to a duvet. What tog should I get him?
Thanks!