Based on our findings, these e-cigarette cartridges may contain quantities of nicotine ranging from zero to almost 7 milligrams (mg). Toxicology references state a dose as low as 1 mg of nicotine may cause symptoms in a small child. 16 mg of nicotine represents a potentially fatal dose of nicotine for a 25 pound child.

Nicotine, even at low doses, is quite dangerous to small children. A few milligrams of pure nicotine may cause symptoms of:

nausea,
vomiting,
diarrhea,
drowsiness,
weakness,
irritability,
sweating,
increased heart rate
and blood pressure.

Higher doses may lead to coma, seizures, depressed respiration, irregular heartbeat, lower heart rate and blood pressure, and even death.

http://ipcblog.org/2010/09/14/the-truth-about-e-cigarettes-a-potential-poisoning-hazard/