DS5 has just had a lot of fun with a complicated >1000 piece lego set (with adult help), and also with keva contraptions set (planks, balls and building guidelines come with kit). He's very gentle and can play with fragile things (as intricate lego items can be!) and repair them when needed.
Any suggestions on other building kits that he might enjoy alone or with an adult? Maybe something with some electronics? And preferably something that could be built upon and have components that can be used in other ways rather than a stand alone item?
Beak
