Some time ago I had seen a kid play with stacked cups and I pointed out to the parents that the base of the cups had animals on it. only recently did I learn of the advantages of a stacking cups both as a play and educational toy.
These stacking cups are colourful, made from recycled milk jugs.
Not only do the cups have numbers on them based on their sizes but also add up in volume. Fun and math can go hand in hand when the kid can learn 1+2, 1+3, 1+4, 1+5, 2+3, 2+4 filling water or sand and emptying into bigger cups.