So, do we have a reasonable expectation of privacy when we are out and about in public? No. Not unless we are doing something intrinsically private. Does a child have a greater right to privacy than an adult? Well... Courts the world over, are generally more protective of the rights of the vulnerable, including children, than those of John Smith or Jane Doe.
We've made a new sport of catching people out, posting and tagging photos of them in situations that were private, and not meant for mass-consumption: flesh spilling over a swimsuit, a chocolate-smeared mouth or cocktail-fueled moment. Then we spend hours trolling Facebook with an open window onto other's private moments.