Or, admit that you wanted to sew a fanged animal onto your child's clothing as a costume, and since really any animal will do for such high-concept art, a koala found at the local thrift shop allows one to pontificate about koalas' diet and aggressiveness.
Step 1: Get Cheap Stuffed Animals
You won't believe this part: I bought the koala for $1, and before starting in on my costume idea, tossed it into the washing machine. After the spin-cycle, I heard a faint song coming from the washing machine. Upon opening the door, imagine my surprise to hear "Take Me Out to the Ballgame" in beepy monotone emanating from the koala. Not only had the electronics survived and then been activated by the washer, but someone had put the unofficial anthem of baseball into a marsupial native to Australia!
Step 2: Cut Open the Mouth; Sew in Fangs
I made the koala costume first and didn't take in-process images. Plus, I figure a toddler is a more attractive intro image than the dog on my butt.
Here, I've cut the dog's mouth, and hand-sewn in felt cut into the shape of teeth.