Apple brings age verification to UK users in iOS 26.4 beta - Users who don’t verify their age may not be able to download or purchase apps.
(www.theverge.com)
There is.
It's called Parental Controls.
It also does a fairly good job at preventing stuff from getting through.
One of the big issues right now is that there's a lot of sexualized content on social media right now that's bypassing parental controls because the social media services are doing a poor job of limiting that content when encountering a parental controlled device.