I am letting parents know that I discourage kids from playing games faster than 15 minutes with a 10 second increment (that means each side gets 15 minutes to make all their moves and gets an additional 10 seconds after each move). Sometimes we have to play a little faster in class because classes are only 30 minutes long, but playing a bunch of 10, 5, and 3-minute games daily is not a good habit. A 30-minute time control or longer is the ideal.
When I was a kid, I was playing 1, 2, or 3-hour games around once a week and this is how I really improved. I learned how to think long and deeply about a position—considering the various options, calculating their outcomes, keeping my mind open for new realizations and insights after thinking about a move for 5, 10, 20, even 30 minutes.
I also would not suggest playing more often than three 15-minute games or two 30-minute games a day. We do not want chess.com to turn into a video game that stimulates but does not educate. Chess Chevra's goal is to help kids become deep, thorough, sharp, and creative thinkers. Playing fast games or too many games can be counterproductive towards this goal.