This is such a silly issue on a governmental level. Shouldn't the parents, who spend more time around their children than the Florida House of Representatives does, worry about and monitor their own children?
Off the top of my head, I can think of two reasons why it might be preferable to have the government intervene.
1) We are happy to have the government intervene in other cases for the sake of children; I would be pretty upset at any politician who espoused removing age restrictions on cigarettes. I don’t know that social media is as bad but it certainly has some of the addictive properties
2) An argument from tragedy of the masses: if all kids’ social lives currently revolve around social media, unilaterally disallowing one child to use it could result in alienation from their peer group, which might be worse for the kid than social media. A government mandate would remove this issue.