yes, they began making lego's and Knex systems that work together.....I personally LOVED the Knex and Legos in the home for our boys.....they have been the longest lasting "toy" in our home :o)
My advice.....invest in the 2 galloon baggies BEFORE purchasing anything new :O) The most frustrating part of legos/knex is keeping them sort of together so your "genius" can rebuild his favorites. I always kept the boxes, too, that they came in, and used them to put all the pieces into the baggie THEN back into the box. My oldest (now 13) was a lego and knex "champ" and loved and wanted EVERYTHING made. He was so easy to buy for because there was always something new. It just got to the point where we have a whole small AREA and 1/2 a closet for these items!
I know this sounds "anal", but at one point, we had SOOOO many mixed up legos that we divided them by colors into baggies and plastic drawers. This way, they could find pieces according to color on their instruction sheets. BUT... if i had known to get larger baggies ahead of time, it would've been alot eaiser! It would've never gotten to that point, though, if I had taught my son how to put his legos away from the very beginning :o)
The best thing we did was invent a medium travel box of "loose pieces" of legos and then of knex...this allows creative building anytime/anywhere without mixing up the pieces from a set :O)
"Training" is key for your son. If you teach him how to put his legos/knex away everytime, then he will be a happier kid later when he pulls it out again. And you wil be a happier mom helping him find the pieces he needs :O)
Oh yeah....my "rule" about the knex (because some of them were so large).....he was allowed to keep them up for 3-4 days, then clean them up. Some creations can take them anywhere from 3-6 hours of building, and my heart couldn't "destroy it" after all that work :O)
The creativity is ENDLESS for these products and if your son is interested in them, I highly recommend them in your home.
Merry Christmas!
~N. :O)