This is a tough topic.
We know that there are bad actors pushing bad messaging on social media and we also know that children are more impressionable. This is why they're so heavily targeted with advertising, because it works really well on them.
So, now we have a situation where social media access is exposing children to informational weapons produced by adversarial nation states. Like advertising, this is targeted at the younger demographic. They're more credible, have less life experience to spot bullshit and have more free time to spread the message once they're afflicted (infected?) with whatever meme is being pushed on them.
We, as a society, understand that there are some things who's harms outweigh the benefits for children and we restrict them to adults. Sex, alcohol, tobacco, porn, owning firearms, joining the military, etc. These are things that can cause harms well in excess of what a child can grasp and so we restrict their access to them.
Social media is becoming increasingly harmful to everyone and that needs to be addressed at some point. Until then, we can at least reduce the impact to people by not exposing them to it while they're still so impressionable.
I don't know the best way to do this but limiting exposure to the toxic environment that is social media seems like a reasonable stop-gap measure until we, as a civilization, can figure out how to deal with this new form of media.