A relative of mine is a nurse working in a hospital. I noticed a long time ago that her perspective on the statistics of illnesses is very skewed. She sees only very sick patients because -- duh -- she works in a hospital. Hence, she thinks every sniffle of her nephew is an emergency -- because she sees only emergency cases!
There are ~40K dead, ~100K wounded in Gaza by the war, of which half are children: about 70K child casualties of which 50K didn't die.
Parents and hospitals will prioritise children over adults. A child with multiple gunshot wounds will more than likely die on the spot and not be taken to hospital. A child with a single gunshot wound is more likely to cling to life long enough to make it into a hospital. In absolute terms, the few dozens cases mentioned in the article are just the inevitable statistics. I would be very surprised if doctors in Gaza had not treated many more such cases! I would expect a couple of hundred per hospital (there are only 32) at least.
To reiterate: None of this is in any way good, none of the children deserved any of this, and in no way is Israel innocent in the matter. It's just that it is the natural consequence of warfare in a high-density urban setting with that demo.