When playing Overwatch (or Hearthstone), they can end their current game and log out. When playing WoW, they should head to the nearest inn to log out. These games take place in real time and children are usually on some kind of team with other players; if they leave before the game ends, they are probably putting their teammates in a more precarious situation. No, it's not the same as keeping the peace in the middle of the third quarter of a basketball game, but it's still a competitive activity between children who have created a camaraderie with each other and are working together to achieve a goal.
Don't abuse your knowledge (that you can't pause an online game) by accidentally trying to get more game time. Because, as many parents may not understand, these online games are live, can't be paused, and players trust each other. But, they claim, they're in the middle of a game, can't they finish first? A parent has gone viral for arguing that, yes, they should be allowed to end their game and he's right.