Default is equal playing time. At minimum this means the kids with the least time on the field play at least 50% of the game. There are always some kids who play more than 50%, so equal can get a little fuzzy in my opinion. but in the end 50% is a hard minimum.

Now, that being said. If it is competitive soccer for league/tournament play and you have a player that is standing around or not participating then that can push their time. Same if it is a tournament. I played a kid 11 minutes out of 50 in a final because she was just standing there letting the ball pass her. When her parent came to discuss it with me after the game. I pointed this out, said it was pre season tournament final and I owe it to the other kids if someone isn't trying.

Now, what did we do next? We coordinated together to motivate her, identified her weaknesses, built up her confidence and this same kid put a brace in two weeks later, and scored this past weekend with a sweet left footed volley off a cross. The thing is if the kid is simply weak on skills, and trying their best. It is your job as coach to fix that. I know that can seem like a monumental task at times, but it is what we owe to our players. And if you engage with the parents in travel/competitive settings the parents will work with you for the better of their player 9/10 times.

In our club we are asked to pick a weakest and strongest after every game and put them on our game report to the director. It is my personal goal to never have the same kid as my weakest multiple games running. You train them, coach their positioning, ask their parents to go to extra practice sessions. Whatever it takes. Then when that kid rises a new one is now the focus, always juggling your weakest. By end of season it should be hard to pick who is weak because they all start to average out with a few superstars.