I’d let the game breathe more.
With seven players you can still keep minutes fair without changing somebody every five minutes. Longer blocks give the children time to settle into the game, make a mistake, recover and actually experience the position they are in.
I would plan the first couple of changes before kick-off, then watch the players rather than the stopwatch every 30 seconds.
You can track minutes afterwards if fairness is a concern. That usually tells you more than trying to make every spell identical.
Rolling subs are there to help you include everyone, not to make the touchline feel like an ice-hockey bench.
If a child has only just started getting involved and your alarm goes off, it is fine to wait a minute and make the change at a more natural moment.
