Wouldn't know. I don't have to constantly tell my children or beg them to do anything but my DD has ADHD and is sensory and the result is that she can be a bit fidgety, not jumping in her sit or kicking the seat fidgity, but she pulls on her clothes, and fidgets in her seat, etc. I know plenty of adults who are fidgety as well but that doesn't mean I want to subject a stranger to that. Sad part is that people who know my children say they are exceptionally polite and well behaived and when we have flown gone as far as saying they didn't realize a child was near them. They would and I hope most adults have enough manners to NOT tell someone, whether it be an adult or a child, to sit still and shut up. That is certainly how to get a 5 year to break down in tears. I know my DD would tell another child that is not a polite thing to say to someone. Last I checked most young children need some gentle prompts or reminders, even the best behaived, I am not talking about begging bc you don't parent, THIS aside from safety IS the reason most parents want to sit with their children so they can be sure they do not disrupt those around them. But it would never cross my mind to tell a child or an adult to sit still and "shut up".
To the poster who said they wouldn't move but would shut them out. I hope you will be understanding when a child accidently spills their drink or gets sick. That shouln't be your problem but the parents job to take care of them. I might not fly for business but I have flown several times a year from all over to US, Asia, Europe, Hawaii etc for almost 40 years. So yes I am not a new flier. But I only fly airlines like Delta, jet blue, etc where I can pick a seat but even the best plans can be changed. I have not flown Southwest bc I hate not knowing what I am getting into, but if I did I would buy the early bird deal. And yes I have had several adults spill their drinks on me so it is a possibilty, esp with turbulance, or just plain by accident. I also know that it is difficult for a child or adult to get in and out of their bags. Many kids I know don't sit with a gaming system at 5,6 but do bring books, art stuff, etc. So they will be in and out of their bags since I don't want a bored child.
I notice that IRL people are not nealy as rude or cranky as they seem on these boards. I guess what leaves me
is that if I want to be a good parent and ensure that my children are respectful and so I want to stay with them there is something wrong with that. I am not speaking about older children but more like 5,6 etc. I think some seem to feel children are 2nd class citizens. Seems a bit damned if you do or damned if you don't. Btw I have seen more inappropriate adults who drink too much, curse, be rude to the flight attendants and passengers, shout, etc, then children. Maybe, I just have been lucky. Then again I have also moved my seat for families and never once wondered why they didn't plan better. Travelling solo or with my DH I have been moved many times when I have planned in advance. Btw I too prefer an aisle seat as I am tall and not a tiny person. But I guess for me personally I would rather have a child sit with their adult than listen to them crying for their mommy the whole flight. I will say I have always been asked in the most polite way. Not sure if I would feel differently if I was told I have to move rather than excuse me can you help me out. I should also add I would not expect the airline to sit the 6 of us together since 4 are adults but I think if moved from our booked seats either 2 kids with one adult or 2 and 2 seating. I used to fly to MI from NY once a month for 2 years and many families would end up getting separated when their detroit flight was late and they gave their seats to standby bc they didn't think they were coming. Northwest was horrible with that.