How about ... don't bring young children on airplanes unless absolutely necessary
They went to visit her GRANDPARENTS.
How about everyone with kids stays locked in the basement until the kids are 20? What were they supposed to do? The kid was fine on the flight to their destination. How were they supposed to know the kid was going to throw a fit? Were they supposed to say "OK, I think the kid is gont to cry today, I guess we'll just cancel our return home & I'll miss my work tomorrow?"
It's impossible to know when a 3-year-old is going to go off. It happens.
Maybe they could have picked the kid up & walked around to calm them, but it sounds like the stewardess wanted that kid strapped in its seat. Which probably would not have helped calm the kid at all.