If you were scared to travel with a baby, the real fun begins when you travel with a toddler. Let's just call traveling with a toddler "unpredictable." There are a few tricks over the last couple years that have helped my 13 hour flights or 3rd connection be less painful. None of which include drugging your child, but stuffing them full of pasta and making them extremely tired might be some of them.
Let your child walk (run, skip, roll) as much as possible, this reduces the need for your child to run laps around the plane
When you have connecting flights, make sure you have enough time to catch your next flight (in the airline's magazine, you have a layout of your arrival airport, check out the map of the airport so you know where your next flight's gate is)
Sleep! There has been a theme here, but the easiest way to get through a flight with your toddler is some good ol' ZZZzzzzz's. Do not drug your child, but a full belly and lots of running around helps!