Why are children susceptible to iron overdose more than an adult?

lol, children are more susceptible to any substance overdose than adults. Their bodies are small and they carry less blood. Think of how much alcohol it takes to get an adult intoxicated. Maybe a few shots? After a few their blood is a certain percentage alcohol. Now look at a child, they have less blood. All it would take is one shot and that same volume of alcohol makes their blood the same dilution.