I'd agree - with Ford I saw in him that he had an energy/toughness level that many kids didn't have - so I exploited it. The summer he was 4 I started him on harder hikes and by end of that summer he had been on many 10+ mile hikes often with 2-3K of elevation gain. I never carried him (I couldn't!) and he always had a pack on.
He started backpacking with me the next year and by 7 had done trips with up to 18 miles in a 24 hour period.

Is that for all kids? No! But if you get a natural hiker, take it for all you can get

Ford is 12 now, considerably taller than me and can out hike me. Not a bad place to be!