Cross-sectional correlational studies cannot establish causation and it's entirely possible (frankly, likely) that more deprived kids spend more time in front of a screen because their environments are less stimulating/interesting/safe.

This is the same as quitting smoking or just not thinking about an elephant. You can almost never cease/stop doing something, yet you can almost always displace it with something else.

(Disclaimer 'altacc suggests: I do have kids.)