These balls develop: Sensory through textures & colours, Fine Motor Skills through varied sizes, and Gross Motor Skills through bounciness & getting babies to move around. This set includes 1 of each: 4'' Sensory Opaque Ball, 4'' Sensory See-Me Ball, 7'' Sensory Opaque Ball, 7'' Sensory See-Me Ball. All Balls are BPA & Phthalate free, sold fully inflated and can be re-inflated. Colors may vary. Ages 6 months and up. (Set of 4)