Just Bento

I've never worried before about packing soup in a thermos; it has always seemed really straightforward. My kindergartener has just requested miso soup for his lunch. I'd love to send some, but I'm nervous about sending a thermos full of hot soup for a little guy (fearing scalds).

Is it safe to pack it less than boiling, piping hot? Or should it cool down between 6:30 and 11 am enough to be pleasantly warm instead of scalding?