I was 19 when I drug home a 1983 Honda CX650 custom from behind a friends house. I think my parents thought I'd never get it running because half of it was on the trialer and the other half in the back of my truck; but I was home from college for the summer and had been working full time so I put a little money into the thing and got it to run very respectably. My mom was less than thrilled and my dad kept it hid pretty well. I had never had a dirt bike, and this 650 was honestly the first motorcycle I had even been on. I started riding it around the back roads and in the pastures (dual sport CX650!) to get used to it, and eventually worked up to riding it into town (Shreveport, LA; a fiar sized city). Got my endorsement (a joke), had some close calls that taught me about the dangers of being on two wheels and then sold it when it broke and I was out of money to throw at it.
I tell that story to say that you know your kids better than I or we do. If they want to rid eon the street, are fully invested in the idea then teach them, If they are ambivalent or chilly to the idea, let it rest. Full commitment is 100% required for safety in traffic. They have dirt experience, so the mechanics of riding should be firmly in place, therefore I think the most maturing experience for them is to be shown how to ride on the street in a safe and rational way, if they are interested. Yes there are risks, but they are far lower than for someone like me who just took to the road with no guidance at all. Plus I think if you remove from MC crash stats, all the low mile/year riders, drunk riders, and those with significant dirt experience, you are left with a much lower risk overall. Just remember that statistics are great for describing data, but mean nothing for the individual.