Covid is highly unlikely to be dangerous to kids, as far as we know. This much I can agree with, but we don't know if there are any long-term effects, and we won't until sufficient time has passed for that to be discovered. What if it makes kids under the age of 10 sterile ? (No, I don't think it does either, but it's an example of something you can't tell for a while).
And, however unlikely, with a sufficiently large population of kids being infected, there are some who will pay the ultimate price, it is a potentially lethal disease after all - and that utterly sucks if you're one of those kids' parents; I wonder how they feel, when people say "it's no worse than a mild cold for them", looking at their dead child one last time before burying him/her.