“Your kids will hate you now but will thank you later” is a crass rationalization that attempts to justify adultism.
“Justified adultism” (aka “righteous adultism” or “pious adultism”) would be anytime adults think they are implicitly and inherently right in doing something for, to, or at children and youth because they are adults, and young people are, well, young.
Well-meaning liberals, ill-conceived conservatives, and people of all ages employ justified adultism all the time to rationalize schools, parenting decisions, technology access, etc.
That’s as opposed to “power trip adultism” (aka “high and mighty adultism” or “adultocracy”), which doesn’t bother to justify itself. Instead, power is simply, automatically and autocratically foisted onto the shoulders of people over 18/21/25 simply because they are recognized as adults.
This is used to grant driving licenses, alcohol purchasing ability, and voting rights to adults, and exclude all young people from the same. Powertrip adultism is less apparent in general behaviors throughout society though, since the old lady scolding kids for riding bike through the road median flowerbed doesn’t really happen anymore.
However, where it does exist it tends to be hyperbolic, ie sending teenage youth to adult jails for teenage crimes.
The line between these two appears arbitrary – AND MIGHT BE COMPLETELY SO – to young people themselves. Ask a youth!