Probably the best way to avoid motion sickness or air sickness to practice some preventative measures before you get in a car, train or plane. These are simple things to do with lifestyle that you and your kid can do to ward off the possibility.
For example, for two or three days before the flight, avoid eating and drinking the wrong things, and try to avoid overindulging as well. Do feed your kids or yourself very spicy, heavy or overly-fatty foods or foods that you know from past experience can cause upset stomachs.
While on the flight, try to avoid dairy produce (because of the protein and fat content) as well as vegetables and fruits because they may make a stomach unnecessarily acidic.
Some studies have indicated that foods which contain too much salt may exacerbate airsickness as does food which is too rich in vitamin B1 such as pork, beef, eggs and fish. It also appears that if your levels of vitamins A and C plus iron are too low, this might make you more prone to airsickness as well (especially women and children).
Also, don't fall prey to drinking too much just because it does not cost you anything to do so. Whilst there might not be a cost in monetary terms, there could certainly be a cost in terms of sickness if you overindulge.
Even foods that you know are likely to have a strong smell should probably be avoided whilst in-flight because a strong smell is often enough to turn your stomach queasy. Do not wear strong cologne or perfume for the same reason and if you are travelling with a companion, ask them not to refrain as well if possible.
When you are booking your ticket or checking in, try to choose a seat where there is likely to be the least motion. Generally speaking, this will be the middle of the plane in the area of the wings, so if you can get a seat here, it is likely to offer the least disturbed ride.
Avoid letting your kids read on a flight because as anyone who has ever suffered motion sickness will tell you, having your eyes fixed on a book a few inches away will only make it worse. Its best to keep your eyes fixed on the horizon outside the plane.
On most planes, there will be an air vent above your head so make sure you use it. Having a flow of air on your child's face and head will help to keep you cool and refreshed to at least a certain degree.
Try to keep your child away from people travelling who are suffering airsickness if possible as hearing others chatting about how bad they feel just doesn't help.