Lawn is signed exactly like yard, which is also the compound sign for park, i.e.,grass, and area combined.
To sign grass, hold your open hand under your chin, with palm facing up and fingers spread out and curved. To sign area, take your dominant hand, with fingers spread out and palm facing down, then make a counter-clockwise circle in front of your body.
Teach your toddler the lawn sign when you want to engage them in outdoor activities and help them identify areas of the house and property.
This is a useful flash card taught best in conjunction with other home and garden signs.