medicine is not an exact science!

7.5+5.0 is certainly within the safe range.
When some one forgets to shake the medicine, the variation
of the amount medicine could change by more than that, therefore the dosage given on the bottle must take those variation into consideration to give a much large safety margin. The time interval between taking the medicine also
reduces the risk in your case. In any event, I would say
the risk your child was exposed to other virus in the
two emergency rooms (also very small) are greater than
the risk of overdose.

I suggest you to have a more balance view of life and spend your time to take care of your child instead of
trying to punish people.