Sounds like a typical kid to me. Probably hot, tired, cranky, needed a nap. After the slap on the behind, of course (smile).
I watched the video. The kid was acting like a normal 19 month old who was hungry or tired or just couldn’t sit still. He wasn’t kicking and screaming. He was just a little fussy.
I think the airline should first fire the air waitress (they go ballistic when you call them that), offer a public apology, and give them some first-class tickets to wherever the family wants to fly. It’ll be a lot cheaper than going to trial.