Agree on the board rules before the first turn: who starts, whether an exact roll is needed to finish, and how extra turns work. Then keep one visible player turn at a time and count moves together.
In Snakes and Ladders, most outcomes depend on chance. With children, the skill to practice is counting and taking turns, not inventing a winning strategy. Treat a snake or ladder as part of the story, then move promptly to the next player.
A steady rhythm prevents more disputes than a complicated house rule.