I have flown with my kids many times from the age of 5 months onward. One tip I read that has been very useful is to plan to have one "new" toy or object to play with every 20 minutes of the flight. It doesn't have to be a new item, although I have a whole set of travel toys/trinkets that are used only for flights so that it itsn't something they always play with. Another tip was to wrap each item in inexpensive wrapping paper, because it takes them additional time to unwrap! I've covered a 10-hour flight this way.
Also, if you child has ear pain and trying to pop it doesn't work, ask the flight attendant to put a folded paper towel/napkin in a cup and add just enough water to soak it but so no water drips. You then place the cup over your child's ear, and the warmth can help lessen the ear pressure.
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