If kids live past 30, they’ve reached the point we stop worrying about them as much, but everyone’s an individual. One of our boys was dating a new gal about the time he turned 30 - he was quite smitten and she loved concerts. Every dime of extra money would have been spent traveling to cool concerts and living like hippies - with enough money they would have quit their jobs until the money ran out. Our other boy was hooked up with a drama queen who was all into big houses. He would have used the money to get into a house he couldn’t afford, or landscapes that look like something off of Pinterest and half the plants would be dead now. They have a few well off relatives and will inherit 6 figures, and knowing in advance that will eventually happen may not help their decision making when the day comes - all we can hope for is they aren’t in between relationships when it happens and having some rebound crisis.
I’ve had remodeling clients off all ages who came into money one way or the other - some remodel, some buy new, some developed coke habits and were broke in 4 years, some are trust fund slugs that stay drunk and play video games, some have a stupid expensive car or RV that they can’t afford to own or fix, some buy a cabin and it rots without maintenance, some buy a boat and that’s a hole to pour money into, some buy an airplane that sits, some build a giant shop and fill it with toys and payments they can’t afford, some buy a condo in Cancun they get tired of. I’m sure someone has used the money to pay off bills, or do constructive things with and it’s just not as obvious.
My personal bias is to inject money at multiple times for multiple worthwhile things, rather than fund some weird new hobby in a big lump sum like collecting swords or cosplay costumes. Do things that encourage good decision making and stability, and that’s different for every kid or grand kid.
If you want to give a kid a great education in investing, if they actually own a wide variety of individual stocks, funds, etc. that can’t be touched, they look them up and follow them. Rather than one simple number at the end of the year, they naturally want to learn about each company and what impacts it. Even a conservative fund vs growth fund reinforces what they are good for. I know a dad that funds a little every month of his 20 something son’s online trading - he knows the son will blow the money, but it’s an eduction the son puts a lot of effort into.
Beware of the finance scams that allow kids to cash out future pay outs for pennies on the dollar - many will gladly take one donut today rather than two dozen in 10 years.