Short flights with kids in tow are bad enough without adding several more hours on top of it. If you are planning on a trip that involves a 10 hour or more plane journey to get there, you will greatly benefit from the following advice:
Be realistic
Being realistic will help you in the long run. Board the plane with expectations of crying kids, vomit everywhere and spending a good portion of the journey either changing nappies or bringing your little one to the toilet. This will mean that it can only go up from here.
Bring snacks
Bring snacks and plenty of them. While you can pre-order the kiddies menu on most flights, you know what kids are like – even if they picked the meal themselves, they no doubt will turn their nose up when it arrives. This is where your supply of snacks come into play. Make sure they are your kid’s favourite ones as well.
Sweets are ok
On a regular, normal day, using sweets to get your kids to sit down wouldn’t be recommended, but on a plane it’s different. You are in a confined place and there is nowhere to go. So a few jellies is ok to get them to settle.
Bring headphones
Bring your own headphones, just in case. Most airlines supply them but some may charge and there might not be enough. To avoid any panic or issues, just bring your own. Avoid the ones that stick in the ear as these can be pretty annoying for little kids so get kids' style ones that will sit on their head.
Set rules
Set ground rules before you even set foot in the airport. Obviously, this only applies for older kids but be clear from the onset that you won’t tolerate sibling fighting, tantrums or messing. Allocate seating prior to boarding and if possible have an adult sit right beside them. 
When kids are involved, the start of the holiday does not begin as soon as you leave the house - it definitely doesn't start until you have touched down.