More screen time equals less happy kids, or so the dogma goes.
I can't speak with the rigor of an academic study, but I would imagine that the correlation would be contingent on the form of engagement that occurs in the social media use.
When social media serves as a digital extension of self, providing accessibility to a close-knit circle of friends and family with whom a healthy relationship is shared, the correlation should be positive. (Anecdotally, I also find myself happier the more time I spend doing something else with only the rare social media update.)
When social media engagement is passive and serves as a news feed to impulsively glance through the moment our attention slips away from something else, I imagine the correlation would be negative. Especially if social media insidiously creeps into becoming a standalone source of our entertainment.
Yes, social media can augment a person's likability and their subsequently expanded social networks. After all, vulnerability can be attractive if a person is judged competent at any domain, whether fashion, fitness, or intelligence, for example.
Whatever social media as a vast umbrella does to affect its users might be reflected by The Public Isolation Project, an art piece that features a girl on her phone in an isolated gallery for one month.