Having passed this (typical ) school regularly, it is evident there can be issues with kids on bikes, darting in & out of the crawling traffic, double parked cars, buses & pedestrians in the morning & kicking out time.
But IMO, they pose no more of a safety issue than the kids on foot, running & chasing about, just being kids.
Maybe the real issue, is the double parking of cars, alot of which are half on the pavement anyway, causing blind spots. pinch points, and the passing of traffic oblivious to the children around them.
This scene is played out hundreds of thousands times a day up & down the country, and I feel the answer lies elsewhere, we should be encouraging our youngsters onto bikes, and accept the "cuts & bruises" that inevitably accompany that
Maybe it might be worth considering an enforced parking ban within 200 yards of the school at these times, and let the little darlings that don't ride to school at least get a bit of a walk in!