In the UK - 15 minutes with cloud cover (like you get anything else!) for a normal, healthy adult is just fine.
So I'm thinking in Australia, a child could go from the car to the shops and get enough sunlight for vitamin D.
I believe it's normal for 0-2 to be knock-kneed and 2-4 to be bow-legged and then miraculously normal. Must be all the sunshine they play in!
