MJ does absolutely NOTHING to a child.
My ex smoked MJ fairly regular when she was pregnant. (no cigarettes, no alcohol). Her child was born off the charts. By this I mean, he was bigger and healthier than every other child I saw in the nursery those few days.
He is STILL off the charts with every aspect. Smarter, BY FAR, than kids even in higher grades. Outweighs and looks down on kids his same age. He was 86 lb. at just over 2 yrs of age, and NOT fat......just a stocky mini superhuman.
We taught him to speak 1-10 in Spanish before he was 15 months old. He was walking at 7 months.
Myth: Marijuana causes birth defects
While experts generally recommend against any drug use during pregnancy, marijuana has little evidence implicating it in fetal harm, unlike alcohol, cocaine or tobacco. Epidemiological studies have found no evident link between prenatal use of marijuana and birth defects in humans.(2) A recent study by Dr. Susan Astley at the University of Washington refuted an earlier work suggesting that cannabis might cause fetal alcohol syndrome.(3) Although some research has found that prenatal cannabis use is associated with slightly reduced average birth weight and length,(4) these studies have been open to methodological criticism. More recently, a well-controlled study found that cannabis use had a positive impact on birthweight during the third trimester of pregnancy with no adverse behavioral consequences.(5) The same study found a slight reduction in birth length with pot use in the first two months of pregnancy. Another study of Jamaican women who had smoked pot throughout pregnancy found that their babies registered higher on developmental scores at the age of 30 days, while experiencing no significant effects on birthweight or length.(6) While cannabis use is not recommended in pregnancy, it may be of medical value to some women in treating morning sickness or easing childbirth.
I say the OP shouldn't worry about puffing once or twice.