> Everything would be ok for the 1950 kid youd drop anywhere. He would be fine and happy.
Sure. It was a happy and golden time for everyone.
So, one of the amazing things about the modern world is that actual information is at everyone's fingertips, which I find is better than anecdotal conjecture. A quick google away, I can find this document: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1380550/pdf/amj...
From this we can learn that since 1950 the mortality rate among 5-14 year olds has declined at an average rate of 2% per year, largely due to reductions in accident rates (particularly motor vehicle accidents) and deaths due to disease. Of any group of random kids of that age in the US, in 1950 pretty much twice as many of them would be dead by 14 than in the present day. If they were black and male, in 1950 their mortality rate from 5-14 was one in a thousand. That it's only half that today is... still pretty shocking.
And that's just the changing rate for kids encountering the worst possible outcome, during their childhood. What other outcomes have changed? Well, drop a boy randomly in the US in 1950, and from 1964 onwards there's about a 10% chance he gets drafted and sent to Vietnam. Or we could look at the other end of the outcome scale: If your hypothetical kid was a 5 year old girl dropped in 1950 America, she'd have very different opportunities compared to a modern child - she'd be 24 before the first women were admitted to Princeton or Yale, for example. If your 1950 experiment dropped a gay kid into America, well... if they're lucky, they're in Illinois where homosexuality becomes legal in 1962. If they're in Texas, they have to wait until 2003.
About a third of kids in 1950 lived in poverty in the US. That improved a lot over the 60s and 70s. Nowadays it's... around a fifth. Still shocking, but again, your odds look better today than 70 years ago.
And let's not get into the ethical issues of your 'drop a random kid somewhere in the US' plan where that might result in dropping a black child in Mississippi before the Civil Rights act of 1964, where they would grow up under Jim Crow. This kid would spend 4 years in segregated schooling before Brown v Board (and probably years after that waiting for desegregation to actually happen), and our hypothetical 1950 5 year old would turn 18 two years before the Voting Rights act.
Yeah. They'd be fine and happy.