Many is signed, by showing your many fingers. Start with your fingers made into a fist, then open them up a couple times, spreading out your fingers.
When your child is young, their ability to count will often be limited. So instead, we use the signs for one (when there is a single object) and many (for any larger amount).
For young children, teach many in conjunction with the signs for the numbers one and two. Infants quickly catch on to the differences between one, two, and many, forming a foundation for learning to count as they grow older.
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