This reminds me of the time when I was like 7 or 8. I found a porno magazine in my brother's room, and saw a 900 number next to a hot naked chick. Anyway, I called the number and handed the phone to my cousin (same age).
My mom was super pissed when she got her phone bill. Right away, my brother blamed me for it. Never mind the fact he was the one with magazines in his room.
Got my ass beat and had to pay the fee with what i had saved up.
Anyway, yeah I've had other mobile games try that sneaky shit, where a "buy this" pops up immediately after clearing a stage, etc.
I let my oldest play Candy Crush on my phone and without paying attention, he racked up a few bucks in charges.