It's extremely unlikely that you'd hit any turbulence en route to Turkey so, as far as feeling queasy is concerned, the only point to worry about is during take off. While your son will naturally want to look out of the window, I strongly advise telling him to look straight ahead at the point of take off. Then, once the plane has got well into the air (and before it goes into the clouds) you can let him enjoy the view.
From then on, looking straight ahead, out out of the window will be a good idea. Focussing on something closer, for any length of time, (such as a book) is probably best avoided.
Most children who get travel sick only do so through sideways motion. (That's either because the car is cornering or because they're looking out of a side window). The forward motion of an aircraft is unlikely to cause travel sickness (unless you're very unlucky and get some additional up and down movement through turbulence).
Many (perhaps most) children hate the taste of crystallised ginger but some youngsters love it. If your son is one of those who like it, it's an excellent remedy for travel sickness.
Chris