There are a several classes of medications that can kill a toddler with a single dose. Toddlers are particularly susceptible due to their low weights and propensity to place everything in their mouths.

1. Calcium channel blockers
2. Camphor-containing rubs
3. Opioids/opiates
4. Oil of wintergreen/ aspirin
5. Cyclic antidepressants
6. Topical blood pressure patches (clonidine)
7. Eye drops and nasal sprays (oxymetazoline)
8. Sulfonylureas
9. Antimalarial drugs (cloroquine)

References

1. Morris-Kukowski, C. England AG. Toxicity, Deadly in a Single Dose. Emedicine, Pediatrics.