A 5 year old with little game experience would be happy with any game. Even if they can't beat anything. (Or at least I was like that)
Anyways, I think that this game looks suitable for all ages. (I am 15, and am really looking forward to it. Mostly because I am a big fan of open world type games, action figures, and Disney) I think whoever this kid is, would have a bunch of fun wondering around the different worlds, and they would have a lot of fun playing with the toys. Also, if they like Disney movies, they would get to play as their favorite characters. --- Objection! http://tinyurl.com/c7eeoug
based on the information given on this at this point, it seems you can have a free play mode where you can do whatever you want within the game. I do not know for sure, but it seems like there are certain modes you can play that are completely void of enemies.
Remember, this is just speculation, as the game has not been released yet. --- I still think Pac-Man was the best game and had the best storyline... EVER!!! 'nuff said.