Pretty is signed exactly like beautiful: form your dominant hand into the ASL number 5 sign, holding your thumb to your chin. Then swipe your fingers across your face, from the dominant side to the non-dominant side, until all four fingers join the thumb in front of the chin area.
Teach your toddler the pretty sign in context: when they look pretty in their cute dress or outfit, when you see pretty flowers or birds in the garden, or when you admire other people or children and comment that they are pretty.
Teach your toddler the pretty sign in conjunction with beautiful and nice, in context, so that they gradually understand the generality of the concept whether it applies to persons, flowers, animals, or objects.
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