Answer:
Law of effect.
Step-by-step explanation:
This principle was created by Edward Thorndike and it basically says that responses that generate a filling effect in a certain situation are more expected to happen again in that situation and the other way around with upsetting effects of certain situations.
In the situation above is a good example of this, because the children get happy if they get a sticker but they know it only happens if they deliver their homework. It produces a satisfying effect on them in order to keep doing what provocated that feeling.