Grow is signed exactly like plant: take your non-dominant hand to form the 'pot' by making the ASL sign for O. Then take your dominant hand, forming a flat 'O' hand by making all your fingers touch, have it come up through the non-dominant hand's 'pot' bottom, and finally open up your fingers as the 'plant' passes the top of your non-dominant fist, looking like leaves opening up or a flower blooming.
If you have a yard with a garden, a window box with plants, or even just indoor, potted plants, use the grow sign to teach your baby. Teach your baby an appreciation for these living things so that they grow up seeing the beauty and function of plants in our daily lives. Eventually, you can extend your child's understanding of grow by also showing them that a business can grow, a neighborhood or a community can grow, and so on.
Teach your toddler the grow sign in the context of plants, grass, flowers, and trees growing in your garden. Eventually, you can extend the concept to describe the growth of your family (when babies are born or a member gets married), or the growth of your business.