Duvet tog and 3.5yr old

[WestYorkshireGirl]

I read somewhere that you are not meant to get a heavy tog duvet for children as they have higher temperatures than adults. DD is currently under a 1 tog which I got when she moved out of her toddler bed into a single in the summer, but her room has started to get cold and I am wondering if she needs something more. Any suggestions on where to go for official advice? TIA

Most cot bed duvets are 4.5 tog, so thats what my 3 yr old is under in his toddler bed.
The 5 yr old has had a sheet over the summer, and is now on a 4.5, but I do have a 10 tog for his single if he needs it over the winter (was in a toddler bed last winter)

My 3 year old is under a normal single duvet. 10 tog I think? The cot bed one was like a paper napkin to me
We're thinking of getting him a wool duvet like ours though as they regulate the sleeping temperature.

My 4 year old had a 4 tog on his cot bed & now has a 4.5 tog duvet on his single bed. I may get a 10.5 tog for the coldest winter months, or may layer up with a blanket/quilted throw if needed.

10 tog here. House gets cold and DS is a cold person like me!

I posted a similar thread when I moved DS onto a duvet aged 2.5 and following several recommendations I went with a 7 tog (single duvet). It's been perfect all year round although he throws it off during the height of summer. I couldn't find any "official" advice but I think once they get to 3ish they're pretty good at deciding for themselves what's too hot/too cold.

if it is a single bed then the maximum recommended tog is 10.5tog. Our whole family uses a 4.5tog in summer and 10.5tog in winter

Thanks everyone!