Assuming they are bigger than a lap child, bring the car/booster seat. It's a comfort item, sized for them, and allowed on the plane. Also, they can't wiggle out of a 5pt harness.

Alternatively/also add: a tablet, phone, video or game to distract them if they are just scared. A few hours of video for the flight will not corrupt them.

This situation started long before the flight.

This is why I didn't take my kids on a plane until the youngest was 7. But even when I did, I was a bit worried about something like this.

Thankfully, giving him a tablet loaded with videos he likes kept him occupied. In my experience, don't really on plane Wi-Fi! It's always sucked (been unusable) for me. Someone else here mentioned about bringing candy/snacks, which is also a very good idea.

My son is autistic and stubborn. I could totally see him doing this. I'd try to get him to keep it on but if I can't, I'm taking my family off the plane. It's not reasonable to delay a plane full of people under any circumstances.

I am late to the party, but an item I haven’t seen is: prepare the kid.

We have flown a bunch of times with our kids. The days before departure, there are “drills”: lengthy explanations of what will happen, getting the kid curious, answering their questions, reading stories of kids traveling. It means that, once we get there, the bulk of the experience is not fully unexpected, so the kid doesn’t freak out.

We never had massive tantrums while traveling, only standard hungry/tired cries we usually managed in a couple of minutes, with any bribe that would work.

One thing that helps a lot with take off and landing is to get them to swallow some liquids or eat a small snack. This lets them equalize their ears to the changes in pressure. Those can be very painful if you don't instinctively do it (like kids) or if you have trouble with it.

Any kid may do this in an unfamiliar environment

1. Parents need to be prepared with distractions
2. Normally have an escape plan. For example if you were going to a restaurant, decide ahead of time which parent takes the kid outside
3. Since there is no escape plan once you’re on an aircraft, don’t take a little kid flying if at all possible.

We only took a little one once, at an age when nursing is a great distraction plus made him sleepy. Otherwise, we drove or didn’t travel longer distances.

The reality is any kid may misbehave in such a scary environment. You may think the parents are entitled or poor parents when they don’t do something about it but the reality is in an airplane your options are limited

I have three kids, all within 2 years.

We did not travel on planes because I always though people with small kids in planes acted like entitled assholes.

That family will now face a lawsuit from the airline. Someone has to pay for that flight.

Benadryl.