Maybe there's a case that parents can track their own children, though I hate the idea.
But that surely cannot extend to other children (i.e. the boy/girlfriend).
My mother was very much the "helicopter parent". The result was that friends never came round to my house, but I'd go to theirs and simply lie about what I'd done. "Why are you so tired?" is as easily answered with "we stayed up until 10am playing Warhammer" as "we drank three litres of wine and played GTA2 until dawn." Even my best friend's parents agreed my mum was terrible in this respect, and they'd fabricate cover stories if we'd gone out drinking somewhere and my mum phoned.
I think government agents certainly are permitted the same: it's called "shadowing". I know, reasonable suspicion and all that, but within the confines of a parent-child relationship, it is the parent that holds all the power, including the ability to define what "reasonable suspicion" means, and to act on that definition alone.
So no, I still don't see the fundamental difference between a parent claiming "I reserve the blanket right to monitor my childrens movements" and a government claiming the same on its citizens.
(edit: not saying they're equal, there certainly are differences in scale and execution -- but the fundamental policy is still one of distrust and subversion)
From the ruling:
"The Court rules that the Constitution permits law enforcement officers to remotely and continuously view and record an individual’s front yard (and the activities and people thereon) through the use of a hidden video camera concealed off of the individual’s property but only upon obtaining a search warrant from a judge based on a showing of probable cause to believe criminal activity was occurring. The American people have a reasonable expectation of privacy in the activities occurring in and around the front yard of their homes particularly where the home is located in a very rural, isolated setting. This reasonable expectation of privacy prohibits the warrantless, continuous, and covert recording of Mr. Vargas’ front yard for six weeks."
I don't need to record your property to see who arrives to and leaves from your home.
Having that ability is also convenient, even if you can't use the evidence in a court of law. It could lead to obtaining evidence that can be procured in legitimate ways.
Parents are permitted to sit on their porches and wait for their children to arrive home.
Government agents aren't permitted the same right.