last i read kids (~7 and under) didn't have "fully developed ACE2 receptors" which lead to the spike RBD not fully binding in young children. this allowed their immune system to fight the invader and gave them very strong protection against SARS-CoV-2.

mutations could bring about a spanish-flu style pandemic in the young so i agree it's not a good time to get comfortable yet.. but i'm not sure i agree with mRNA vaccines being forced on all (especially kids) without long term study data. especially when subunit and inactivated vaccines for the S1 protein now exist