If they want to do a multiplayer game with robots, I'd prefer a more RPG-like setting. For example, you're not constructing your robots to force them to battle other players' robots (it would be a complete ripoff...), you own a robot you created as your character and do various tweaks to it, and you need to form a party with other players to battle AI party.
Pros:
- There could actually be a catching plot. Let's say that you're an unknown hero from the streets (+Yun's idea) destined to save the Earth from evil aliens and their robots with the help of your comrades. And it will be much better than just a game with robot battles - given that the target audience are children, well, who doesn't want to be a hero?
- The gameplay could be really flexible - you could go as solo warrior, or form a party, you could play against the AI or against the players who claimed to be on the enemy's side.
- Microtransactions, of course.
- They don't need to go all-out about customization (as it would disrupt the balance), and instead force the players to master their skills, making it a real competition.
- In any setting the game doesn't need a server, it could use the host-peers scheme.
Cons:
- Done wrong, it could easily override the main concept of the "small game for middle schoolers" and made the game very costly.
- It would be VERY resource-demanding (why, hello, Ahagon... would you like to remove that AK-47 replica elsewhere?... pretty please... I certainly do not like the look in your eyes right now...) even without the graphics part.
- You'll need a long-term support for this type of game if you want people to remain being interested in it.