A few things to note on Japan and kids walking around. Usually you don't see children that are less than 5-6 years old walking around doing daily errands. When it's children that are younger it's usually with the parent walking a few meters behind to monitor what the child is doing.
And, Japan had special usage phones for children that would track their location even back in 2004. I lived there back then and I know a few parents who used that for their young children. So, yes children are allowed to freely roam around at an early age which is great but Japanese parents are not adverse to tracking.
And, Japan had special usage phones for children that would track their location even back in 2004. I lived there back then and I know a few parents who used that for their young children. So, yes children are allowed to freely roam around at an early age which is great but Japanese parents are not adverse to tracking.