I'd make a multiplayer game focused entirely on making friends and comrades through some fun shared activities. So many games create toxic online spaces and a big part of it is the basic strategy and mechanics of those games. e.g., Overwatch tries to get you to work as a team of specialized players with a hyper-competitive objective. Random anonymous teams almost always suck and start crapping on each other.

Imagine if kids playing games actually helped them socialize and build empathy.