I'm pretty sure that if the parents are reminded that the captain could divert because of their children's behaviour (what would happen during an emergency?), they'd get them straightened out ASAP.

However, I for one are all for cabins with no kids. Not all flights, just flights where the airline has more than one flight, and then offer that cabin with just adults. Also, where there are more than one F or J cabin available on a single aircraft (747/380), arrange for one that is child free.

Now having said that, there are adults out there who behave like children too, but at least the FAs can deal with them directly.