Cheating is dishonest. It violates trust between the cheater and the person cheated. In school, cheating disrespects the authority of the teacher and the school. It also contaminates the feedback that grades are meant to give, warping the school's mission of providing teaching and learning. Start communicating household rules to children early in their lives.
Consistency is all-important.
As soon as they are able, children should be helped to understand the purpose of the rules that they are expected to follow. Sanctions for rule breaking should be calibrated to the child's age as well as to the frequency and severity of the violation. Children of all ages should be given assignments around the house, even if, for a very young child, it's just to bring a dish from the table into the kitchen. Assignments should be modest, age-graded, and regular. Household tasks should not be so time-consuming as to interfere with schoolwork or other activities important to them.