Baby On Board

For the life of me I don't see the point of those stickers on cars proclaiming "Baby On Board" and the like. What are these people trying to tell me? Are they saying that I need to be careful not to get too close to their cars - something I tend not to do in traffic anyway? Or are they warning me that they may be distracted by their offspring while driving and may become a little erratic ... in which case, what the hell are they doing on the road in the first place?!