If the risk was meaningful, they would have been getting the vaccine already. But yes, there is tons of unnecessary risk we apply to children every day, but we still do it (I don't think you need the whole driving statistics spiel). We measure risk by acceptability, not by existence.
There's not a lot of data. ACIP found that there was more severe illness than vaccine side effects in 12+ age groups (with a disclaimer that the group had less data due to less 2nd doses being administered):
