Not only are they UGLY, but those people look crazy! As a person driving behind you, do I honestly need to know that you are a heterosexual couple with two identical, crazy-eyed daughter children and a dog?
Not that I have anything against children, dogs or heterosexuality (apart from my allergy--to dogs, that is), but I don't see why I someone feels the need to have it hieroglyphicized all over the back window of their Ford Windstar/Chevy Venture/whatever scary soccer mom gas-guzzler he or she is driving.
Maybe it's like those signs you see in people's windows that are meant for firefighters: "We love our (2) cats, (3) dogs and (4) GERBILS ." Perhaps the intention of these icons upon the ass of a minivan are a mobile parallel for these signs. Say the car flips over and the ambulance comes and the EMTs have to pull everyone out from the depths of the "safest car on the road." Can you imagine that conversation?
EMT 1: Well, John, it looks like we got everyone out safe and alive.
EMT 2: OMG! Like, look, there's a puppy on the back window! You have to go back in there and get him Mike! If you don't he'll die! DO YOU WANT THE PUPPY TO DIE?!?
The worst version of these tiny stick figure role calls are the ones that actually have the family member's names underneath the icons. This version is not only obnoxious and tasteless, but dangerous. A child abductor could be lurking around the grocery store parking lot and do his research on your family quickly and effortlessly. When he walks up your daughter he will be prepared:
Abductor: "Hello little 'Cindy,' I'm your Uncle Barney. Your mommy 'Cynthia' and your father 'Chuck' told me to come get you from this produce section so we can go walk your puppy 'Sassy' and play Legos with your brother 'TJ.' "
Poor little Cindy will be so dazzled with familiar names that she won't think twice about trusting Uncle Barney. We all know how that story ends, and it ain't with TJ and Legos.