People who understand their religion deeply pass their faith on to others by the way they speak and act. They may "witness" in formal and informal ways in their community and spread their religious beliefs in this way. When someone is excited about something, that enthusiasm can spread quickly those others.
As an affirmation of the strength of parents' instruction and example, there is a large family in our town in which the older children attended a religious-affiliated school. Since religious instruction takes place every day at this school, the parents did not have any instruction in the home, although they practiced certain religious rites and encouraged the child's adherence to their church's doctrine. However, as the smaller children grew older, they went to the public schoold because of changes in the religious school's administration and curriculum. Since the children did not receive religious instruction at school, the parents sought to give instruction and reinformcement after supper each day. Now, as adults, the young children are much stronger in their religious faith than the older ones who attended the parochial school.
Like all cultural concepts, religious ones are instilled in the children by parents. For, they are reinforced in the strongest of ways within a family.
It's true that technology can help people stay connected or get connected to faith, as in locating a suitable place of worship after moving. What is different about religion/faith is the personal commitment and sacrifice which is generally required by adherents to that faith. Because of that, I agree with #2 that learning about faith from one's family is the best way to promulgate a religious belief. Add to that teaching and education through programs of the faith, especially those geared to children.
With the ever increasing use of technology, these world religions now have a greater advantage than simply passing it down to their children provided. Now other people from other countries have greater access to the information regarding the religions. For example, forty years ago, someone seeking spiritual enlightenment would have had to travel far and wide to stay connected with a religion like Buddhism. Now they can connect and stay connected through the use of the internet.
By teaching it to their children. People who are religious instruct their children in that religion. My parents, for example, would have our family saying prayers together before I even had any true idea what I was saying in those prayers. We went to church every week and we would observe all the major religious holidays at home (not just by making Easter eggs, for example, but by making sacrifices for Lent, things like that). This is the most effective way to pass on a religion, I think.