So now I have to work harder at speaking to her in Farsi. Seeing other children speak Farsi has a great impact on them when they are 3 or older. I hope this helps. And the tape can be played to the baby when the baby is about to sleep. The taped content will be retained in the child's mind for a longer period of time if is played before to sleep, as it could be the last activity baby does before going to bed.
Songs are a nice way for kids to learn a language They have fun and learn.
You can play them in the car, while driving or at home. A third option I would think of is as Soheila recommended, finding Iranian play mates. Find out from your community centre, if any Iranian groups are meeting. Or maybe, and hopefully, anyone here lives closed to you and has children about your son's age. All the best.