The add sign is signed with both hands. Hold your non-dominant hand steady, forming a flat letter O sign (with the thumb side facing you). Your open, dominant hand starts a short distance from and lower than the non-dominant hand, as it appears to scoop something as you draw all four fingers together with your thumb. Then set your dominant hand to just under your non-dominant hand, now both signing a flat 'O'.
Teach your child the add sign in the context of basic counting or simple mathematical exercises in everyday life: like adding something to their food, your shopping cart, or the the toys or flash cards they are playing with.
This is a useful flash card taught best in conjunction with ordinary activities that necessitate counting or adding something.