Clonidine? (movie goof)
Unless the mother thought her children were suffering from high blood pressure, she probably meant to prescribe them klonopin instead of clonidine. Also, a dosage of 10mg of clonidine is 100x the normal dose (0.1mg) and most definitely would have been effective at killing her children due to such a drastic decrease in their blood pressure.
Funnily enough, even had the mother meant to say klonopin, the max dosage is 2mg, and not 10mg.