These are not your grandpa's blocks. The Water Set, with its sealed windows filled with colored liquid, can be overlaid to show how colors mix. And the Twisted Blocks transform triangles into parallelograms, allowing kids to turn angles upside-down with a quick flip of the wrist. If this sounds familiar, that's because color mixing, shape exploration, and spatial experimentation are all big cheeses in the kindergarten curriculum. These sets keep things playful, and safe. Made from recycled rubber wood, any shots of color come from nontoxic soy ink and all glue is of the non-formaldehyde variety. The perfect green gear for an impromptu block party! (Plan Toys, various sets priced from $20- 40: Twisted Blocks Set $29.95, Water Blocks $29.95, Creative Blocks Set $29.95).