I side with the parents on this. There was no warning of the 15 minute window previously, so after they enter their password allowing their child to download an app, how would they know it remains password free for 15 minutes?
I don't expect every parent to be technologically literate, and with Apple marketing themselves as family friendly, they should've tried harder to make the App Store family friendly ages ago.
Maybe they should just include something in the setup screens:
Is this your first iPxxx?
Are you scared of technology?
Are you scared of technology?
and then address settings from there.