If your child runs out of eg. cough syrup, your house has got an exactly the same medicine prescribed to your child previously, but this is prescribed to an adult but unopened, would you feed it to your child? At the dosage stated for your child @3.5ml.

Agree with the other mommies, if it's the exact same medicine and your child has no previous issues taking it, then yes I'll let him or her take it. I'd use the spoon prescribed previously with my child's medicine to get the same and exact measurements (if you haven't throw it away that is).