Smoking marijuana during pregnancy?

My fiances sister smoked marijuana throughout her pregnancy, and occasionally cigarettes, and her 3 year old little boy has been sick his whole life. He's had constant ear infections, and has really bad breathing issues, he always sounds very nasally. Do you think she's a big part of him always being sick? Im 37 weeks pregnant and stopped the second i found out I was pregnant. And i know smoking marijuana breaks down your immune system, so i imagine it does the same to your baby whenbpregnant. Thanks.