Children tap the textured balls to light them up and keep them lit for 1 minute. They can then roll them on different surfaces to observe changes. The balls have a calming effect and develop fine motor skills, teaching children about cause and effect. They feature raised designs great for mark-making. Set of 6 balls in 3 different designs. Ø 8.4 cm. Require 3-4 hour charging time with the USB cable provided, for 4-5 hours of use.