As to 1) The prisoners dillema is a pretty basic example of how the best possible co-ordinated action is not necesarily the best possible individual action. i.e.
other kids not on social media/ your kid not on social media Δ0 happiness
other kids not on social media/ your kid on social media Δ-3 happiness
other kids on social media/ your kid on social media Δ-10 happiness
other kids on social media/ your kid not not social media Δ-50 happiness
Maybe some form of co-ordination might be in the parents best interest... maybe some form of representative could do something about it if it's in the kids best interest?