While we have covered the theory of cam toys and crank toys, as you know theory and practice are different things :) So in attempt to look more into practice and because cam toys are rarely sold in web stores, I'll try to help you build some of them yourself - providing the best info from this site and other sites too!
How To Make a Hatching Cam Toy
This is a cute little visual guide showing how to make a hatching cam toy and how it's not as simple as it look.
Nevertheless, the guide is easy to understand and follow. Be prepared for 1 to 4 hours if you want to build a cam toy that works well.
This page at the Technology Student site points out several pitfalls peuple do when making cam toys themselves. Check it out before you start work to save wasted hours and materials.
A Simple Cam Mechanism
This is a great very detailed tutorial for building a simple cam mechanism. The link takes you to a PDF download (sorry the old link disappeared). I think that even primary school pupils can manage with it.
The toy itself isn't as neat as the chicken but the guide explain perfectly the cam toy logics.
This PDF guide is also not bad - the toys there are a bit rough, but the explanations are good, although not very well illustrated.
The guide claims you only need 30-60 minutes to complete the toys.
The rotation of these toys won't be as precise as of the hatching toy but they are intended to be big so kids should be fine with that.