I don't agree with age verification, but there isn't anywhere 'set your children's ages in their device accounts' that limits their access to inappropriate content and social media.

You can set age in Google Accounts, but they can access pretty much anything when they reach age 13 (which is about the age a lot of these things start to become a real problem) and as a parent you don't have any way to limit that. They don't even need to ask to install new phone apps.

Children also use computers as well as phones and you don't want to stop them using a web browser! You also obviously can't supervise them every moment they are online even if you wanted to.