Click first then ask permission
(East of Toronto, Ontario, Canada)
I have begun making candid photos of strangers (while in public places.) I usually stand back a good distance and use a telephoto zoom lens. Usually they are unaware I have even taken a photo. After I have what I want, I walk up and tell them I have taken their photo. I tell therm I would like to keep them but if they do not want me to keep the photo, I will erase it. If it is children in the photo, I ask the parents.
(Caution: Some municipalities e.g.. Toronto have by-laws forbidding the making of photos in which children are the subject.)
I have never had anyone ask me to delete the photos. Most are pleased I take the trouble to ask. Some want to see the photos which I always show them. I have even used done this with a couple of bikini clad young women who were playing in a heavy surf.
As far as I can tell, the worst that can happen is I will be asked to delete the photos. I believe this procedure is legal in most jurisdictions. If anyone has information to the contrary, please post it.