I think its all about knowing how you should behave. The first people to be blamed are the adults since they teach the children. So actually adults are the ones who should switch mobiles off and sit in darbar properly.
When I was little I was told how to behave in a darbar. I remember wanting to walk around the stage like the other little kids. But my mum told me that I should sit next to her and not move as we had come to see maharaj..I used to go punjabi class and most kids would go langar hall and I saw all my friends in the langar hall however my mum did not allow me to go out until diwan finished.
The difference now a days is children are not being taught which place they can meet sangat. In darbar we are not there to socialise...we are there to connect...socialising etc can be done outside.
The thing is my mum explained. Even though at the time I complained loads like how my legs were tired, how I did not understand or how other people were not doing it. My mum instead ignored all that and decided to teach me how to sit, how to fold my legs, where to put my hands, my head, eyes closed etc. Even in ardas she taught me the right way to stand. The amount of adults I see doing ardas in the wrong pose still amazes me today....
Anyways when I was little we used to be the last people to leave we stayed all the way till SGGS ji was put to bed. Langar hall would be empty by this point, sometimes no one to serve.....looking back it was this disipline which made me a sikh. When i first went gurdwara I did not understand what they said as they speak a different style of punjabi.
Being told a discipline of you must sit and stay till end made me listen, which then made me understand....its like how some people can understand hindi from watching lots of bollywood films. Likewise from repeated regular watching and listening I began to understand katha and my mum made it into a game cos on they way home she would ask me to tell her the katha....but this all happened very slowly and only due to the intial discipline.
I therefore do think parents should encourage their children to be the better one who sits. Its just like how parents encourage children to go school. When children go nursey they tend to cry alot. No parent considers that forcing or being strict likewise the same applies for diwan...knowing how to behave in darbar means you learn more and become a better sikh...just like how each parent will tell their child off when they are not doing well at school.
The last thing...classroom = to learn from our teacher. Darbar = to learn from our guru. Outside of school = to play, Outside of gurdwara = to play. I feel the crux of the matter is our attitude and understanding of darbar. We learn from childhood how to behave in a classroom, meeting etc....darbar is no different.