Dumping and pouring is fun! Toddlers explore gravity and weight by dumping toys and bins. Along the way they learn about cause-and-effect, muscle control (to not pour all of it out), and self awareness as to what their bodies can do. And, toddlers crave the sensory experience that accompanies dumping toys! Dumping toys also trains large muscle groups to be more controlled, and that is a precursor to fine motor skill development. You might also fine preschool aged children who also dump toys, and for the same reasons as above!