It's getting less and less limiting as time goes on.
I don't disagree with this point.
But it doesn't change the fact though that at this point in time - at all points in time actually - if one chooses to qualify only for an auto drivers licence one limits oneself to only a selection of available vehicles to drive.
That's why my answer to the question as to whether it's a waste of time to learn in a manual was "maybe".
It will be down to individual choice at the end of the day, based on what each individual projects will be their needs or wants from driving in the future.
Yes, there is more to master when learning in a manual. It will not suit the wants, or indeed needs, of many. But if a manual car is chosen by the OP his kids won't have limited choices at the end of the process.
Good luck to them in their future driving lives, and to the OP with the decision making.