Okay, so Orreed and I were plotting for our Marvel characters on the Camp of Disney thread, and this is what we came up with:
Odin didn't want the Tessaract(Cosmic Cube) to fall in the wrong hands when he got it back after Thor returned after the Battle of New York with Loki and the Tessaract, so he put it in a vault with a certain amount of keys (one for each of the Young Avengers) and locked it, then hiding the keys within the very souls of each key's keeper. Each key represented good qualities/things the wielders of the Tessaract should have (seven things, like maybe trust or responsibility, whatever, we can come up with a list based on our characters' personalities), and upon doing this he received a prophecy to explain things to the key keepers and predict an outcome, etc.
Anyway, Thanos or whoever secretly contacted Loki in prison and decided to give him a second chance after Loki told him of this. They are using Luke to find the key keepers, and sent him to the camp because the prophecy pretty much said it would find them there when translated.
The Avengers sent their kids there to see if they would bond without them, because they were considering buying a mansion somewhere where the kids could all live together and go to school and stuff with Jarvis looking after them so the Avengers could do hero stuff without worrying (that would be an awesome sequel btw) and they thought the camp would be a good indicator, they really hadn't intended to ignite the prophecy. But they did, and soon the Young Avengers start figuring out what's going on and discovering their keys. Once they actually discover their key, it comes outside of their soul and turns into a key necklace that can't be broken or taken off.
(I don't know where Luke fits into this part) Then, once they have all the keys, a disaster happens, so they have to go get the Tessaract to stop it, only to find out that was a diversion and Loki and Thanos capture them and try to make them open the vault so they can get the cube. A fight ensues, our parents come to help, and we defeat them.