The only challenges that are even remotely difficult are the Egg Roll ones and once you have the technique for them, they are a doddle. I actually got told off for putting the difficulty at 4 originally so I changed it to a 2.
Seriously, this is NOT a difficult kids game. There's even videos on Youtube if you're totally stuck on the challenges. Saying this, someone once complained Ben 10 was not easy so what can you do