It tends to happen when you really don't need it; you're hungover, you're tired, or you have shedloads of work you need to get through before you land. Yes, we're talking about a flight where a troublemaking child is seated near you - and they won't take no for an answer.
Here's how to placate the child - and its parents - without getting into any potentially-embarrassing situations.
The excited child:
In a way, this is sort of sweet - until they start kicking the back of your chair in a repetitive fashion and shrieking about everything they see (the clouds! The toilet! The head steward!). Telling it to calm down won't work. Our advice? Shoot one or both parents a warning look and go about your business. Directing your wrath at the child will, in this instance, end badly.
The tearful child:
In order to solve this situation, wait until both parents have gone to the toilet or are otherwise distracted. Then address the child firmly yet quietly, saying something like: "We are all a bit cold, hungry and tired. I found the meal equally tasteless, and now I have to go to [insert where you're travelling to] to finalise my divorce. Stop squeaking." The child should either stop dead in its tracks or cry harder; either way, you've got nothing to lose. NB: This approach will not work on a child under three.
The fidgeting child:
It's time to play the passive-aggressive card. Beckon over a steward and say "I'm trying to sleep, but someone close to me won't keep still. Is there any way I could be moved?" If luck's on your side, you'll get an upgrade, and if not, at least the child and its parents have been notified of the issue.
The talkative child:
Take it easy on this lot - they're bored, but they're not playing up, and they probably find you fascinating. A lot more fascinating than 'Just a swift triple at Gatwick' mum and 'Let me finish my book' dad. Broker a deal with the child by purchasing some extremely chewy sweets from the trolley. They will remain in your favour as you've bought them an edible present, but they'll be too busy chewing to bother you.
Disclaimer: This advice is meant as a humorous guide only and probably should not be used in real life. Ever.