Public Transport

Between Amsterdam Centraal and Zaandam is by train and a ticket costs EUR 2,80 (return is the price of two singles). Zaandam to Zaandijk (for the Zaanse Schans) is also easily done by train, costing EUR 2,40.
An easy way is to buy all the necessary train tickets in advance at www.ns.nl and print them at home. It is a little bit cheaper than buying from a machine at the station, and saves your parents struggling with the instructions and - perhaps - finding out not having the required PIN code on their credit card.
For local transport in Amsterdam separate tickets are possibly cheaper than a (multi-)day pass, depending on how much travelling they plan to do. But they should realise that Amsterdam is a very walkable city: the city centre is compact (half an hour to cross it from the Centraal Station to the Rijksmuseum) and walking is the best way to enjoy all the canals and houses along them.
The GVB website gives all the possibilities. The tourist information in front of the Centraal Station will undoubtedly be able to inform them further.

We are visiting Amsterdam now and all the public transportation is EXCELLENT. The only thing to warn them about is that the tickets and passes must be scanned by a machine both on entering the bus, train, tram, or metro AND when leaving --- this is really easy to forget. Even though they will see everybody doing it.

Nancy is so right ! If you don't scan your ticket upon LEAVING , the maximum price for a ticket will be charged on your card .

With the trams, one thing to maybe make it a bit easier is that you do not need to wait until you are actually leaving to scan out. As soon as you leave the station before yours, you can do your out-scan. Once I saw you could do that, it made things easier as I could get everything ready (I was there in March, so it was cold and I had to get the hat and gloves on, the jacket zipped up and the hood up :) ) and then just walk out.