You're the first person online/IRL to recognize this subconscious insensitivity. I don't really blame people though, it's more the culture.
But, the real reason why people think childhood is better is because most people SUCK AT ADULTING.
Adulthood is sold as a bohemian big boys club where any desire you have must be fulfilled no matter what.
Things like the future are seen as apocalyptic because it involves you fading away from a new generation.
Adulthood was about responsibility and building up for future generations, but that changed in the past couple century lies with the invention of suburbia and neoliberalism.