Had when i worked in a preschool and kids love them! I would use colored sand instead of white salt. DIY salt tray with alphabet cards. Easy to make and kids have fun smoothing out the salt after correctly making the letter
PRESCHOOL MATH IDEAS: cut pieces of cardboard and drew the shapes on them, then used a hot glue gun to make the shape, so the outline 'popped out' on the paper. Then place under paper and rub crayons over top to reveal shape.