Continuity mistake: After the mermaids splash Wendy with a ton of water, her hair is wet and you can tell because it is sort of hanging down and drooping. Then they cut away, then when they cut back to Wendy, her hair is perfectly dry.
Continuity mistake: As Wendy is singing 'Your mother and mine' she lays Michael down. As she is laying him down, her nightgown turns white. The next time you see her, her nightgown is blue again.