Child-free planes are never gonna happen. Airlines have a limited number of slots and they aren't going to use one of them to duplicate a route just to exclude the handful of kids from a flight. In any case, for the majority of passengers they book a particular flight because it's the cheapest, so even if the airline did offer a child-free flight for more money most people wouldn't take it.

As a leisure traveller I wouldn't pay more. I would suck it up and put up with whatever happens on the plane to save myself hundreds of pounds. As a business traveller, well, I actually went to the trouble of running this by my boss as a theoretical scenario. He said that there is no way I would be allowed to book a more expensive flight for the same route unless there was some sort of operational benefit to the company. And no, potentially being a bit less tetchy does not count as an operational benefit.

As I'm sure has been said a thousand times of FT, when you exclude the kids, the DYKWIA's, the drunks, the recliners, the snorers, the window-blind-messers, the perpetual peers, those who hog the arm rest, the sockless, the shirtless, the loud-headphoners, the chatters, the heavily-perfumed, the malodorous and any number of other quasi-offensive individuals from what it, essentially, PUBLIC transport then you have a... now what's it called again??? Oh yeah, a private plane. Dig deep. They're not cheap!