Even if the adults are not able to restrict themselves, they are still responsible for the well being of the children who don't know better, at least until they are past the point of reducing cognitive, critical thinking and reading comprehension. A four year old doesn't know better.
Effects of Excessive Screen Time on Neurodevelopment, Learning, Memory, Mental Health, and Neurodegeneration: a Scoping Review
https://link.springer.com/article/10.1007/s11469-019-00182-2
Evidence suggests that chronic sensory stimulation via excessive exposure to screen time may affect brain development in negative ways. Excessive smartphone use may increase the risk of cognitive, behavioral, and emotional disorders in adolescents and young adults that also has the potential to increase the risk of early onset dementia in late adulthood.
https://healthmatters.nyp.org/what-does-too-much-screen-time...
Early data from a landmark National Institutes of Health (NIH) study that began in 2018 indicates that children who spent more than two hours a day on screen-time activities scored lower on language and thinking tests, and some children with more than seven hours a day of screen time experienced thinning of the brain’s cortex, the area of the brain related to critical thinking and reasoning.
Sure, they won't call it 'brain damage' - just reduced cognitive reasoning and critical thinking.