It's been a looooong time, but I used to travel with four children. All the advice above looks good, to which I will add:
Be self-sufficient: Planes are large and full these days, and cabin staff is smaller. Your children's needs may happen when no one can get you water or a snack or something entertaining. Clumsy as it may seem, carrying your own supplies can pay off.
Keep some things hidden: if you're not lucky enough to be able to get the kids to sleep through most of the flight, the toys or games may become boring. If you can put them away, and take out something else, it helps.
Gum: not for the baby, but if the 4-year-old can handle it, it helps with changing pressure on take-off and landing.
Stay calm, ignore boors: If you've done all you can to prepare yourself and the kids for the trip, and something goes wrong...that happens. And if anyone gives you grief about it, don't let them make it worse for you. They were babies once, too, and if they have nothing better to do than complain to a parent trying to cope--they still are.