Children commonly try to steal toys, food, or money from parents, friends, or a store. Before age 4 or 5, children don't understand "ownership." Prior to that they consider everything "mine." Fortunately, they can't conceal stealing well during these early years.
Clarify your expectation. "Don't take things that don't belong to you, because the person they belong to will miss them and feel sad."
If your child steals something, respond as follows: