You can skip the speculation and just Google the MSDS and look for the LD50 value. Thanks in part to the Right to Know act, millions of animals have make the ultimate sacrifice to help you make more educated decisions, and what quantity/weight will kill half of the sampled population. This from Prestone...
ACUTE TOXICITY VALUES:
LD50 Oral Rat: 4700 mg/kg
LD50 Skin Rabbit: 9530 mg/kg
LD50 Oral Rat: 12,565 mg/kg
LD50 Skin Rabbit: 11,890 mg/kg
So with the presumption that your body is like a rat, and you weigh about 80kg (176.37 pounds) you'd need to ingest 4700*80= 376,000mg, or 13.26oz., to die about half the time.
For a 9kg kid of pet (20 pounds), the math works out to just under 1.5oz. Yes pretty serious..