well just as an example, look at food.
Kids like simple tasting, simple looking food.
As soon as you start dressing food up and introducing complex flavors, they don't like it.
Secondly, even as you said they look more cartoony, so do all the covers now that I look more closely. Look at the handegg players' legs. Look at tiger woods' arms. Hardly any muscle definition. Same goes for the footballers.
But yes, kids like simple things that portray reality as they see it.
Same goes for any art style. Kids tend to like things that look like natural (this does not mean realistic). Adults tend to appreciate all art styles, but you'll be hard pressed to find children you like cubism, modern, and abstract art.
However, if something is "fun" then kids will like it. For example, surrealism, dinosaur shaped nuggets, and stuff like that.
Then again, a lot of kids are scared by surrealism.
Additionally, look at what the 360 sports covers portray.
In order from top,
It is an adult thing to be moved by emotionally targeted art.