I assuming in this activity I am one of the teachers and my goal would be to encourage exploration and discovery through play, in a safe environment. I would always start with rules.
Preschool: with an apron only, small half way filled water play container outside with colorful pit toy balls mixed in with toy dinosaurs, using their hands. Small group adult supervision required, find only the dinosaurs.
Modified for Toddlers: put an apron on the child. Fill half way with water play tub outside with only colorful pit toy balls, and saying its okay for them to use their hands. One child at a time with an adult supervising, the child then finds the balls by color. The teacher can prompt and teach in this