To be blunt (please forgive), I think that view comes from the infantilization of children that, in essence, originated in mid- to late Victorian times, specifically in England.
For the 120,000 years of H. sapiens' existence prior, 'children' were understood as equal members of society. Capable of widely independent, and 'responsible', action -- hunting game on par with their 'elders', running and playing together responsibly without 'adult supervision', indeed groups of 'children' with no adult accompaniment at all going out and successfully taking down very big -- and dangerous -- game to feed the tribe -- need I go on?
I myself grew up in a 1960s-suburban translation of same. Which came from parents being farm-family types, where such behavior of children was taken for granted. In summer, out of school, after breakfast our parents gave no thought to our going out of the house and disappearing -- into the nearby woods, into other friends' houses, what did it matter? -- until lunchtime at home. And then back out again.
From age five, my parents assumed I knew how to keep myself alive through whatever kind of (again, summertime school vacation) entertainment out-of-doors I found interesting.
Including that they assumed I knew how not to be shot by the fairly numerous deer-hunters who peopled the thick woods behind our subdivision all through the fall and winter! (I knew to buy bright-red winter coats. )
Point is: We are all being infantilized into the state where we could elect [yes, given all the irregularities etc.] our current Orange Orangutang.