Responsible parents have always worked hard at keeping track of their kids and to see if they are being truthful when they report in about what they have been doing. This involved having kids call to check in or it required parents to be calling their children to see where they are and what they are doing.
Social media has made tracking your kids easier than ever before. If they use foursquare or any other gps social sites you can see where they are checking in to follow where they are, when they arrived and even when they leave.
Twitter lets you follow their tweets to see where they are going and see when they post their updates. Facebook is even better for seeing what your kids are doing when you aren't around. You also have the ability to be friends with your children's friends. It doesn't take a huge amount of detective work to see what your kids post, look at pics and then also look to see what their friends are doing to determine if your kids are doing what they tell you they are doing.
Since its inception social media has evolved and different groups and businesses have found ways to use it to their benefit. So it shouldn't be surprising that parents have also found ways to make their job easier. Social media can be a parents' best friend.