Is it normal for a toddler to hit, and what should you do?

It is extremely common between one and three, because they have intense feelings, very limited language and almost no impulse control. It is not a sign of aggression as a trait. What works: respond immediately and briefly — stop the hand, say clearly that hitting hurts, and attend to the child who was hurt; teach the alternative when everyone is calm rather than in the moment; and look for patterns, since hitting often clusters around tiredness, hunger or transitions. What does not work is hitting back to teach a lesson, which reliably increases the behaviour.