How hot does it have to be for it to be risky to let 2 year old out without a hat?

[suiledonn]

Dh has taken dd to his mother's house for a couple of hours but he didn't bring her sunhat. She wants to play outside and it is staring to get quite warm out.

Dd never keeps a hat on for more than a few mins. It's hardly the end of the world. Are you in UK or somewhere more tropical?

my dd has not worn a hat since she was a toddler. She kept pulling them off but does insist on wearing them in house all the time

my 2 don't have hats as wont keep them on, they both wear sunglasses all the time though.