The title is misleading. This is not about child cognitive development, merely just some brain imaging. In short, the MRI method can not see the effects of screen time. This is of course a good thing but does mean nothing about cognitive development.

From the abstract of the article [1]:

We studied a [...] sample of young people [...] (ages 9–12 years) to investigate the relations between self-reported use of various digital screen media activity (SMA) and functional brain organization. [...] Of principal interest were two hypotheses: First, that functional brain organization (assessed through resting state functional connectivity MRI; rs-fcMRI) is related to digital screen engagement; and second, that children with higher rates of engagement will have functional brain organization profiles related to maladaptive functioning. Results did not support either of these predictions for SMA.

1. https://www.sciencedirect.com/science/article/pii/S001094522...