As you wrote, techs come and go. And will only really help them if they use them (and, to a much smaller extent, to gain more context to understand the other tech they might use in the future)
On the other hand, some skills are always very helpful (especially in our domain, but are also in other domains) and will probably continue to be very helpful for a very long while:
Exploring (any) tech tools, while keeping a focus on this will probably help them a lot over time!
(Another one could sound obvious: «common sense». I am amazed on a daily basis by how many people lack this :D I know I might sound like a troll.... but people how are pragmatic and have good common sense are so much better teammates than the other ones :D
Disclaimer: I don’t have any children, so this is just an opinion based on the desired outcome after a few years, but I guess things are probably very different on a daily basis ;-)