Blackcat, at that age my DS loved building with anything and everything. I agree with the gears suggestion, DS loved them at that age. Marble runs are great- there are many types and most don't seem to require much fine-motor stuff, DS especially liked the wooden block type and one that has stacking plastic tubes, chutes and other fun things. I would consider regular blocks, too- there are lots of cool types; my kids both liked keva planks (the contraptions set especially). Knex is fun, the larger size pieces (can't remember the name, kind of knex junior) are pretty easy to put together, but there are not as complex (read interesting) as the smaller pieces, and they can be pricey. The smaller pieces require a fair amount of dexterity. My kids liked tinker toys and Lincoln logs, too- good garage-sale buys if you can find them. Your DS might even like the oldies-but-goodies building stuff like sugar cubes and frosting, or marshmallows and toothpicks, or pipe cleaners, Popsicle sticks and glue- we went through tons of Popsicle sticks, and it really helps when they are old enough to use a glue gun. You could even get into paper mâché, clay/play dough building, sandbox architecture, etc. Boy- don't get me started, I feel like I spent years doing this stuff (and yes, DS still does it but much more of it is minecraft and terraria now).
