While I do think there would be plenty of parents that would be a bit careless in the sunscreen department. I think most are careful.

I am guilty of not topping up as often as I should but when your having lots of fun the time can fly without realising it. Both my girls tan (thanks to theei getting their dads skin and not mine). I find that in short periods of time, like when they come outside with me when I hang clothes on the line or water the garden are the times I don't even think about sunscreen and those are the times they are getting the exposure, I think you could even tell which side of the car each girl sits on because they are a little darker on one side each.
DD1 is great though, she loves putting sunscreen on and works as a great reminder to me. They do always have hats on outside though. Our rule is no hat no play outside.