If these kids are as spoilt and self-indulgent as their parents, which they might well be, then they'll need fairly constant low level supervision to see they aren't making the journey a misery for those around. It's not demanding per se, or complicated, but it's a parents' job.
If the kid throws up whilst the seat belt signs are on, then the parent needs to be there to clear things up. If the kid spills a drink, the parent needs to be there to help sort it out. If the kid keeps kicking the seat in front, a parent needs to tell it to stop. If the kid reclines its seat into the face of the passenger behind, it needs a parent to wind it back in.
Pay someone to perform your duties or perform them yourself.
And that's without anything on the flight going majorly wrong.