sensory balloon with matching cards. great for teaching 5 senses to preschoolers or keeping toddler hands busy! Except make balloons all one color, or else they'd memorize the color rather than rely on senses to determine contents.
Saw these style boards on Oriental Trading for use as geometry boards. Wondered a diy hack. Use glue on bottom circle of thumbtack to secure it from being plucked out by little fingers. Sowdering About in Seattle: Toddler Busy Boxes