Herd immunity is not a direct goal of vaccination, protection of the individual being vaccinated is. If someone needs protection, then they should get vaccinated!
On the contrary, for the overwhelming majority of children you're absolutely right, they didn't have serious risk from COVID-19, which makes your question a good one, not a rhetorical one.
Regardless, herd immunity was not a serious possibility at any point (given the high Rº and lack of a vaccine that could prevent transmission), which, considering this was known very early on makes your question, again, a good one not a rhetorical one, despite your intent.
Finally, regardless of herd immunity, at risk individuals would still require vaccination, which makes the herd immunity as a goal, again, irrelevant, which is where I started. It's a nice by-product.
I am not sure about America but in India, I was a child during covid, 7th grade - 8th grade and i didn't have a vaccine but my school students just one grade above us were called in school and they were asked for vaccine.
Though, to be fair, my whole family caught a "virus" during 2nd phase except my father but we didn't go to hospital and just bed rest for 2-3 days. My family really were skeptical of vaccine but personally I don't mind vaccines and would prefer it.
