How hard is this OP?
Company A makes game/app/whatever - they have to check content against various rules and regs and state an age range it is suitable for.
Thats their bit done.
If you want free content, you 'pay' for this by seeing the adverts served during the use of the game or app.
If you don't want to see ads, pay the premium not to do so.
Company B supplies apps/games/etc... iTunes, Google etc. THEY may or may not state both the age range for the adverts and the age range for the game (and they may state one but not the other).
They would be the people responsible for selling the advertising space within the app or game.
So you could have a game with content suitable for a toddler, with adverts served that are not suitable for a toddler.
That happens when a game is popular for adults, and lets be clear.. games with in-app purchases like Angry Birds or Candy Crush.. are NOT for toddlers, they are designed and made to sell advertising or to sell in app purchases.. to adults.
Maybe you need that a bit louder - these games are NOT FOR CHILDREN, no matter how animated they are, how many spin off kids films there are, whatever. They are aimed at adults who see advertising and who buy in game content. That is how app/game makers and suppliers make money.
The fact they entertain your children is by the by.