What part of Zombies vs Aliens is "harmless" to a young child of just 5 years old? The game has an age rating of 9+ years old for a reason!!!
The age limit is to prevent children under the specified age from acquiring the game themselves - it is perfectly legal for parents to decide to allow their child to play such a game.
Again, irresponsible parents, using a computer to babysit their child then blaming someone else (Apple) for their balls up.
Parents can't be expected to monitor their children every moment of every day. The parents here acted in a reasonable manner.