What is the effect of smoking pot around toddlers?

Illness. Smoking around infants and young children is healthy. It is known that there is increased risk of ear infections, uri's, pneumonia, asthma and other illnesses. Long term effects can be scarring and damage to the lungs. Do all you can to protect anyone exposed to second hand smoke.
It harms them. If you are smoking pot (or for that matter tobacco) around children, you are exposing them to health risks that amount to child abuse (whether that is legally the case or not). People who do this are either selfish or in denial about the harm they are doing. Both tobacco and marijuana smoke cause damage to developing lungs, increase chances of respiratory and ear infections, and should stop asap.