If you are thinking about practicing yoga with your child, consider purchasing a PVC free yoga mat from lotuspad. They even come in children's sizes (scroll down in the "shop" section to find them).
I entered discount code Fbook1 and received 10% off my purchase. They are currently offering free shipping for orders over $75.
Many yoga studios offer family yoga classes. If you are lucky enough to live in Austin, Texas, Ruta Maya offers free (with purchase) family yoga on Saturday mornings.
