What do you buy them? Lego? Stickle bricks? Well these are a bit different and require the same skills of building things and fixing them together. I first bought these for my son when he was 2 and a half. At first he found it tricky to fit the parts in the holes but a year on and he is slotting everything together himself, so 3-3 and a half is a good starting age. What I like about this toy is that you can build something and make it move. Children can learn about cause and effect - "when you turn this handle this cog turns". Great little toy. The basic set packs away into a smallish box quite neatly.