Oh, Hell no!!
That's an appropriate response for this debate. I don't care how 'safe' you think your colt/stud/stallion is, that horse is not appropriate for your kid or grandkid.
A colt (from here on that's what I'm calling a male intact horse) is full of hormones that are just hoping to home in on a receptive filly or mare. Most studs/colts have nothing that tops the mare scene in their mind and only because a human has them royally bluffed will they keep their dinky in check.
There are a few studs who I've seen (like maybe '5' in the last fifty some odd years) who are so quiet that they even fool people into thinking maybe they are geldings. I've even owned one! I mean so quiet as when they are in the pasture or a stall, they don't talk to other horses and act studdish in any way. Only by checking the exterior plumbing can you tell he's in the altogether.
But to think that a stud is a great prospect for a kid is almost child abuse in my book. I've seen ads like this. Matter of fact, the one snarky email I've had was from a clown who said that his Paint colt was safe for his grandkids...like hell! I wished I had saved it and I'd reprint it but that was before I thought of this blog and I deleted it. If you're reading this, please resend your email so I can post it and we can all have a good laugh!!
To my mind, only professional horsemen should handle a stud. I've stood studs and it was the biggest pain in the neck I think I've ever dealt with. Just have to be on your toes all the time and that's just too much work for me! You can never forget you're dealing with horse hormones. That's one of the reasons that owning a stud is extra liability and you have to have great fences all the time, to prevent problems.
There are PLENTY of mares and geldings out there for your kid. A good kids horse is going to cost you plenty (or should) but still cheaper than dealing with the extra expense of a stud. Don't be fooled by the 'gentle for even kids' ads. Jeez!!
Even if you buy a stud for your kids with the thought of having him gelded anyway, have you ever dealt with the after-effects of gelding?? I sure have and it's a pain also but I much prefer to do that than deal with a stud. Much cheaper to just buy a gelding who is healed up and you don't have to worry about it. There are too many other good horses out there to even deal with this.
Horses are an accident waiting a happen anyway and when you add in the studkins, welp, you're adding in potential trouble. I will say there are a very few people out there who have a way with studs and that's fine but I don't think, from what I've read on CL, that these low class colts need to stay a stud, no matter how 'gentle'...