There's nothing wrong with getting a little messy...
Sometimes it is hard to gauge how valuable a child's experience really was. We can't always observe how the brain is processing information or how the body is interpreting stimuli. But if we see a child whose shirt is soggy and pants are muddy and hands are sandy, then we know that something substantial was happening!
There is something about water and sand and light that calls to many children and the tables that feature these things are often the vehicles for encouraging independent play. Children are also given the freedom to engage in the type of play they prefer (self-esteem and independence). At these tables, toys and space are limited so conflict resolution, sharing and collaboration (interaction and cooperation) are skills that are naturally taught and developed. These skills are more successfully realized as they become more competent communicators, like being able to say, "No, I'm using this right now." or "Do you want to dig for treasure with me?". Thematic information is incorporated and processed through play in these tables. Children become paleontologists digging in the sand for dinosaur bones or use buckets, brooms and pom poms to demonstrate how some whales siphon krill through their baleen (discovery and exploration). Fine motor skills, including eye-hand coordination, are honed while pouring, scooping, filling and building (physical development). The "messy" tables provide opportunities for artistic expression and appreciation as well. Children can make designs in and mold sand, create artwork with colorful water and design structures using blocks.
When seeing a child with sleeves soaked to the elbows and sand in their pockets, the first reaction might be, "I'm going to have to wash those clothes twice!" but take the time to think about the learning that led to this glorious mess.