I don’t know where you live but kids in the UK certainly don’t do much exercise through their childhood

They aren't expected to chase their food until in exhausts and can be easily killed and eaten.

That’s just deliberately missing the point.

It is actually remarkable how quickly we can go from “untrained, can barely go down to the shop on foot without a racing heart” to running being barely a problem (unfortunately to many — it really is hard to burn more energy than what you normally eat with even quite long runs, we are that energy efficient at that).

But the actual point is that people before the agricultural revolution was more than fit enough for that, and evolutionarily speaking that is no time at all, so.. yes, not even being trained from childhood, just deciding to train for that hard, most people could definitely do that.