Sensory play is integral to development, especially under three years old.
The growing child learns about self, others, and the world all around through sensory and tactile exploration.
Cognitively, sensory play is tantamount to baby STEAM class: Science, Technology, Engineering, Art, and Mathematics.
In the social-emotional domain, sensory play is the building of self-concept, self-esteem, and self-efficacy; it is the building blocks of relationships between self and others.
Sensory play makes use of all available fine and gross motor skills, including eye-hand coordination, motor planning, pincer grasp, and instigates the development of new skills through interest and motivation.
Language is given richer, deeper, and anchored meaning through engrossing, immersive play. In fact, some speech therapists, including Rudolph Steiner, founder of Waldorf Education, agree that speech develops through sensory play. Hands (and feet) are linked to speech. So, let them get messy; they are building a brain and a whole person.