Of all the points on which I support children’s rights, their right to own a cell phone is not exactly a priority. I’d say it should be up to the parnts to decide whether their kids should have cell phones - at which point it’s the right of the parents, not the children.
That said I think there might be something broken about how it is solved now - I would probably be in favour of a law banning certain types of software on the phones of children, such as abusive social media or games with microtransactions.