When my DS was 14 months we travelled to Europe. Like you, I didn't want to sedate him but I did want to have the option up my sleeve in case he was distressed during the long flights. He has renal problems and so I spoke to both his paed and his urologist. Both said that either Phenergan or Pain Stop (which contains Codiene) would be suitable, but to try them at home first in case there was any negative effect. Gave Phenergan to DS and my DD (3 at the time) and they both went BESERK. Soooo hyper! Didn't use that on the plane then... Was hesitant to use the Pain Stop and never actually bought any.

In the end the flights were ok. There were some difficult moments, such as when my DS was just about to fall asleep and had that final hurrah cry which lasted about 2 minutes. Until then, he had been quiet. As his mother, I knew I just had to hold him for that two minutes, let him cry and he would finally sleep. The bloke in front of me turned around and said "Would you shut that screaming kid up????" I was already exhausted from lack of sleep and entertaining DS, so I snapped back "Mate, I'm doing the very best I can, it's the first time in seven hours he has made any noise, and if you don't like it I suggest next time you charter a private jet. Now turn around, you're keeping my kid awake!!" He turned around and DS slept for the next 8 hours.... thank god!!!!

Anyway, I wouldn't sedate your DD without consulting your doctor, but honestly you should be fine on a five hour flight. Lots of entertainment as the PP's have suggested... and plenty of patience!!