Autism-Friendly Sensory Large 6 Piece Montessori Gonge River Stones | Primary ColoursStepping stones to better coordination, balance and fun. The River Stones are inspired by stepping stones in a river with each side of the triangle varying in steepness and difficulty. The purpose is to jump from stone to stone without touching the floor you can vary the position of the stones to create more challenging paths for children. Each stone has a rubber rim on the base which prevent them from slipping, and also protect indoor floor areas.