The kid in Iron Man 3 was actually used well.
He gave Tony food and shelter, helped him solve the mystery of the explosions, helped to cure his PTSD and even saved his life.
The actor also gave a decent performance.
I also liked the 2 black kids in Mars Attacks.
When I saw that movie as a kid I thought they were badass. They saved the White House from an alien attack because they learned how to shoot by playing arcade shooters..
Sadly, those are the only positive examples I can think of.
In most cases, kids are just in movies (especially action oriented ones) to be accessories for the protagonist (if the character has kids, people tend to sympathize with him more, even if that character isn't very well developed) or to create conflict (if the kids didn't do stupid things that put everyone in danger, the story wouldn't move forward or would be over very quickly).