Duplo is a toddler-safe version of Lego. Duplo bricks are two times larger in every direction than Lego bricks and are mutually compatible.
Duplo comes in baskets with 2x2, 2x3, and 2x4 bricks with several special pieces like bricks with eyes, slanted or curved bricks and little attachable figurines. My daughter got her first fifty or so pieces of Duplo in a green basket when she was fifteen months old. She learned how to stack them the same day, but could not press strong enough to really hold. By twenty month she was verbal enough to tell us that two 2x2 bricks set in a shift represented a lawn mower. My first son learned his primary colors using same Duplo bricks. My second son by twenty month would stack several bricks in a "tower" and would refuse to go to sleep without it. This Duplo is still around, used with small original Lego. Right now, for example, in my kids' room there is a pair of "penguins" looking more like ostriches: Duplo daddy penguin and Lego baby penguin. Duplo is made out of same secret plastic as Lego: it is tough and hard, pieces don't get worn, loose or discolored over time, and a normal adult wouldn't break them by stepping on. Which can be a missed blessing: my house is littered with sharp undestructible objects, and they are not going anywhere. Rare counterfeit Duplo made in China, as well as readily available Building Bricks are made from different plastic. These pieces are nominally compatible with real Duplo, but dont snap together or with Duplo as well. Building Bricks have cool translucent version, and Chinese fakes have fun parts original Lego never produced, like muddy military green pieces.
Beside basic sets (tubs, or baskets), Duplo has license sets (Dora, Bob the Builder, Sponge Bob, and some others), as well as trains and cars.
See also: children, baby toys, children's toys.