There's about 50 million kids under 12 in the US, so while that percentage looks small that's still ~150,000 kids going to the hospital. I believe the real percentage is probably a bit lower due to underreported infections, but it's worth remembering that even small percentages can have huge effects in a country with hundreds of millions of people.
Yes, given a large denominator rare events will happen. So what?
The relevant argument with kids and Delta is not about whether it happens to some people, it's whether the risk rates high enough to mobilize large scale, disruptive countermeasures.
I can only find data on deaths, not hospitalizations [1], but assuming the numbers are roughly proportional here are things that are more dangerous to kids than Delta:
- Drug ODs
- Car accidents
- Cancer
- Heart disease
- Drowning
- Suffocation
Caveat of course is that the data might be out of date, at least with respect to pockets with high rates of infection
