The real problem, OP - and I think you're beginning to realize it - is that parents want to protect their children forever and there are really only two ways to do it.
First, you can try to protect them their entire lives, which usually eventually involves excessively controlling them, worrying about them, and lots of boundary issues. Second, you can try to teach them and train them in what they need to know to protect themselves and gradually loosen the parental reins, which usually eventually involves crossing ones fingers or praying to a deity and realizing that our kids end up deciding differently than we would and realizing that there is some uncontrollable risk in life and a bad thing or three might befall our kids even though everyone's doing their best to avoid that.
The difficulty is if one stays in the first camp too long, one can really stunt or delay a child's development and growth and it can be practically hard to switch to the second camp. Ideally, one gradually moves from the first camp to the second camp as the kid appears to be able to handle it, with some grace for mistakes, because we all make mistakes and mostly we survive them and make fewer big ones over time.
The advice I was given and try to follow too is that there are really very few mistakes that are non-recoverable: suicide, teen pregnancy, self-harm, maybe early marriage/divorce. Going to a wrong college or wasting $10K or something is fixable.
Yes, it's scary but there is tremendous joy and pride in seeing our kids truly take flight and develop into their own version of adults. If one is lucky, one can also end up having their adult kids be friends and relate to them as adults, which is also really great.
We started off in the first camp for two long with our oldest. We moved to camp two with him pretty rapidly when he went off to college and things didn't go very well. There are other confounding variables with him so it may not have all been due to parenting and things didn't go disastrously wrong. I am still trying to correct my mistakes there. We have done better with the second and third, and they are really doing pretty darn well if I do say so myself.
If it's truly their money, then IMHO you need to teach them the options for how to handle it, along with your advice and recommendations: "Hey Joey, Grandpa Fred left you $100K. We think it would be really wise of you to use that to go to college and get a marketable degree. But it truly is your money and we will love you no matter what." Mentally prepare yourself for them to waste some of it and/or decide to use it in a way that is still acceptable and legal but not what you would have chosen. Let go and watch your children fly free (or bump along the ground a bit with a small possibility of a crash on takeoff but probably not since they came from a good home and were raised well and were given the resources and tools to succeed).
Good luck.