Personally i don't think Candid means taking a photo in secret, it is more like capturing an image that is natural. Obviously if you hide in a bush with a 500mm lens no one is going to see you from that far away but it doesn't mean it's natual. You can be right next to your subjects are the photo can still be natural, the important thing is that they are comfortable with you taking photos.
Most adults have this fear of cameras, they freeze up, stop what they were doing as soon as they spot a camera out of the corner of their eyes. So you either have to be quick to catch them totally unaware or do it enough they don't care at all.
The most sucessful candid capture moments, this moment tells a story of the day of the subject(s)'s life in that moment. There is no rule whether the subjects is looking at the camera or not, some works, some don't, it is all down to the subject and your technique.