Agree on the finish line first
Before play begins, choose a visible finish line: one level, two rounds, or the next save point. A shared plan is easier to follow than a surprise ending.
Give a calm reminder near the finish, then let the player complete the agreed unit when possible. The transition becomes part of the routine rather than a conflict invented at the last second.
Have the next activity ready—a snack, a book, outside time, drawing, or helping with dinner. Ending one good experience is easier when another meaningful option is visible.