At what age can kids be put on the Atkins diet?

The Atkins diet is not healthy for anyone, let alone a toddler. If he's gaining too much weight cut out the junk food and feed him more fresh fruits and vegetables, whole grains and lean whole meats (not ground). A toddler needs a proper, balanced diet to grow and develop properly, if you're not sure what that means you should talk to his pediatrician to come up with a good nutritious diet for him.