When I fly home from the Left Coast, I often take a “red-eye” flight: an overnight flight that leaves at 9 or 10 or 11 p.m., arriving in New York at 6 or 7 in the morning. Five hours in the air and a three-hour time-zone change hacks eight hours out of the day. Add time at the airports, and I'd rather put all that during night hours than lose the whole of the next day. Usually, I get a few hours' sleep in the plane, get home around 8 and go to bed for another couple of hours, and by 10 or 10:30 I'm fine and have the day in front of me.
And the key is that I can usually get at least two or three hours of sleep in the plane. Sometimes it's better than others: two red-eyes ago I got an exit-row seat, and the extra room almost made it feel like I had a hotel room, at least in comparison to the usual knees-up-your-nose seating in economy class. I slept like a baby.
But here's the thing: babies often do not sleep like babies.
Time was, red-eye flights were half empty, or more. You could often spread out on two or even three adjacent seats, and it really was like a little in-flight hotel room. But that time has passed, and red-eyes, as most other flights, are now full or close to full. Things are tight. And as people travel more, they travel more with their small children.
I was on a red-eye a couple of years ago that had a baby crying all night about eight rows ahead of me. That's not hyperbole; the baby really did cry for the entire flight, or at least all of it during which I was awake. I did get some sleep, but I doubt that those in its immediate vicinity could catch any. And on my most recent red-eye, the row in front of me contained a baby who cried on and off, waking me every half hour or so.
Parents: overnight flights are challenging for adults. You have no business putting small children through that challenge, and you have no business putting all the people in the plane around you through the consequences. Trust me on this: there's a good chance that your child will not sleep through the night. There's a good chance that your child will, in fact, be awake often, and will keep you and your unwitting neighbours awake too.
Use this test:
If your child is old enough that you can say, “Honey, you have to be very quiet because all these people around us need to sleep,” and you can rely on the child to understand and stay quiet, then your may take your child on an overnight flight, at your discretion. If that's not the case (and if your child is pre-verbal it almost certainly is not), then do not do it. Fly at another time, during the day. You don't have the right to disrupt the sleep of a plane-load of people for your scheduling convenience.