Have to pick one. Which do you think will be more fun for kids?
Which market are you referring to?
In any case, Zaanse Schans is very child-friendly, I've been there 3 or 4 times and kids are always entertained, especially on the outdoor attractions of the area.
Sorry, my spell check did that. It should say Marken.
We did both. (We biked to Marken and took a train to Zaanse Schans.) I think kids would enjoy Zaanse Schans. There are several working windmills that you can pay a small fee and go in and observe. (when we were there, there was one making peanut oil and one was cutting logs) Both places have a wooden shoe demonstration. The one in Marken was not demonstrating when we were there, but we did get to watch the one at Zaanse Schans and it was very good. Try to watch for a bus tour to be going in...that is when the do the demo. Marken was picturesque, but there was not as many things to do and see. Also, Zaanse Schans is easy and fast to get to. (I think there are buses to Marken...once again, we rode bikes).
I have not been to Marken but would recommend Zaanse Schans from previous experience for the kids. Just did the Historic Triangle (Rick Steves, Page 331) end of March. Another great day trip for kids of any age; includes steam trains, boats, and an open-air folk museum.