It’s amazing there haven’t been thousands of similar mistakes out 400 million doses given.
The kids will likely be just fine. Sore arm and tired for a few days.
I'm surprised this isn't taken as an opportunity to acknowledge and explain the thousands upon thousands of bad reactions ... "it's simply a dosing mistake, no worries. The jab is working exactly as expected. Save for a tiny fraction, they're just tired and achey for a few days. Nothing to see here."
Never let a crisis go to waste, right?