Our Silicone Happy Stacks are the new must-have Montessori toy. Classic stacking cups just got a massive upgrade. This set of 7 square silicone stackers teaches stacking, nesting, counting, and sorting to develop concentration, problem-solving and gross motor skills. They’re great to have around the house, for everything from playtime to mealtime and even bath time. And they nest together, which makes them perfect for on-the-go.