Are the parts from the Erector Build & Play Easy Bucket interchangable with the parts from another set (say the ferris wheel)? In other words, as he grows older and gets more sets, can he use combined sets to to create his own structures?

Erector sets can really expand the imagination. I haven't met a boy yet who doesn't like to put stuff together and then take it apart only to do it all over again. The motorized erector sets are really exciting for them to be able to see something they have put together move and really work. The Erector Build and Play sets are for young children age 5 and older. The pieces are bigger and easier for small hands to work with. The Erector Ferris Wheel set, and those similar, are for ages 8 and up. The pieces are smaller and more detailed and the plans are more challenging than the build and play sets. It is likely that when a child moves up to the regular Erector sets and becomes a "big kid" they will not want to interchange the pieces of the build and play with the regular erector sets. And in fact, they are not interchangeable. We do offer a wide variety of sets for both the build and play and the original erector sets. Allow their imagination to run wild with the Build and Play Erector sets as a beginner and then let them be challenged with the original erector sets when they conquer those.  The Build and Play sets can always be passed along to a younger sibling or cousin to give them hours of enjoyment as well.