er.. I can't find it in Blackwell's: http://www.blackwellreference.com/public/search?query=in+parentis+loco'
in parentis loco means that parents have a right to take control of your life, even if you are not the actual biological parents but can assert in parentis loco.
it is a legal term, if you can find it in blackwell's.
Do you have a reference? Searching Blackwell's doesn't seem to return anything, and google nothing of any use. But you seem so positive, it must be based on something, surely? Just checking this isn't another thing you're so sure about that has no supporting evidence.
As a phrase "in parentis loco" is bad Latin grammar; "in loco parentis" literally means "in place of parents", but that's not in Blackwell's as a (publicly-searchable) phrase, either. However, the whole meaning of the phrase is about people who are acting as parents who aren't, so I very much doubt it has anything to do with what control actual parents have under law.