Why are children in India taught to stay away from their opposite gender?

Indians are hypocrites basically! They believe if a boy and a girl come close it will lead to only one thing! Its strange that for 25 years the parents will ask the children to stay away from the opposite gender but always advocate arranged marriage. Sex is taboo in our country. Instead of imparting healthy knowledge about it the parents believe asking the kids to stay away from the opposite gender is better! But they forget the curiosity tends to be greater when the suppression is more!