The best and largest observational studies don't show a strong correlation. Studies with an intervention are mixed/the effect isn't large. Extreme and compulsive social media use is bad, but it's almost maybe always a symptom rather than a cause.
I saw the trailer for the new Facebook movie last weekend. It's comical really; first people blamed Facebook for the 2016 election and now for their kids being depressed. It's classic scapegoating.
What makes this worse is the irony: in the name of protecting children, we're going to further reduce their freedom. And if there is single largest cause of children being depressed, I'd bet on "lack of freedom" over "social media use".