I agree that a lot of Brits moan a lot about weather in general, and yes we always embarrass ourselves when we have more snow than we know how to deal with!
For me, the difference is risk to health. Rain, wind and snow aren’t going to damage anyone’s health (unless we’re talking floods, hurricanes and blizzards which obviously do present risk, but are more unusual situations, at least in the UK).
I’m contrast, sun and heat don’t have to be at all extreme to be injurious to health. Heat exhaustion can happen very easily (especially to children, whose bodies cannot regulate temperature as efficiently as an adult’s can) and become very dangerous if not dealt with. Sun burn can result in melanoma, rates of which are on the rise in the UK. There is no such thing as a safe tan.
With that in mind, I don’t think children should be sitting in direct sun in high temps, with no shade, for any longer than half an hour or so. Would Australians really sit outside for 3 hours in the hottest part of the day? Without shade?