We flew to the UK last year with our two children - then aged 3 and 1, and given we thought it would be a horror flight, we were very pleasantly surprised that it went so well. At that age they tend to be lulled to sleep for much of the long-haul flight; the same was the case with other little ones we saw on the flight too. We didn't give them any medication; we contemplated it but the chemist talked us out of it, and it turned out there was no need.

So good luck; although it isn't easy taking little ones on a long haul flight, I reckon it won't be as bad as you imagine either....