This varies by region. In some regions, even smartwatch phones must be kept in backpacks. On the other hand, this is a bit of a Finnish phenomenon.
In German-speaking Central Europe, the prevalence of phones among children is remarkably low. In Germany and Switzerland, some children feel they have no use for a phone. My Swiss friend’s child received a phone at age 13 and brought it back on the third day, wanting to return it. They claim that German TikTok apparently gets filled with far-right content very quickly, at least for child profiles.