Up to the highest height

In a true George Banks epiphany moment, I took the day off and we went to fly a kite.

Holly: "Mummy, it's nearly up to the atmosphere. Daddy how high is the atmosphere?"

Adorable, but why does mummy get to go 'ooh aah' and Daddy's left with 'err umm'? I plumped for 30 miles. Wikipedia is my next port of call tonight.