It depends on how adept they are to games at the moment. I think that it has a lot of fun things about it, but you will be setting up the game for them and building things for them in the toybox mode. The toybox mode is as cumbersome as the gameplay style is simplistic. Download some fun Disney approved levels after the kids have beaten the "main game".
They can only be in toy box mode. If you want to see (for example) Baymax and Hawkeye team up, you will have to either download a mission that someone made in Toy box or make one yourself. In fact, only certain characters can join in certain missions. The characters with the A for Avengers on the packaging can be used in those missions. So, even though Spider-Man has been an avenger in the comics, he can only participate in his Ultimate Spider-Man missions. Other characters with the Spider-Man emblem in them are the same way. You need the Spider-Man playset for that. Now, having said that, there are exceptions, but you have to earn them. If you collect enough tokens with a character's face on it (they are scattered throughout the games), you can do things like let Nova play in the Avengers story. Why does it matter? Well, besides the fact that you want to level up all the characters to make them more powerful and enjoyable, each little statue represents a life. So if Hawkeye goes down, send in Iron Man. Once all the characters you have are down, you have to stop playing the story and start that mission over from a checkpoint. The characters do "come to" after a bit and can be used again. To be fair, Baymax was originally a Marvel character from a short lived comic in the late 90s called Big Hero Six. Nothing like the super good movie that just came out. The toy box mode can be a pain, but you can use it to make any kind of game you want: racing, action, adventure, deathmatch. It just takes time.
Don't think so. It just means that the pieces you get are Marvel based. Just buy the characters. Works perfectly fine as long as it is the right platform. Xbox one - Xbox 360, I hear toy box mode still works but that is it.
The standard version comes with the avengers playset and Avengers characters. It also comes with access to the toy box as well. The toy box version comes with toy box access minus the avengers play set. While you can buy play sets like avengers in the future it does not come as part of the package initially. It comes with characters like Stitch and Merida that can only be played in the toy box mode.