I don't remember much but it's an animated movie about these two little creatures, perhaps mice or fish or something. And they are taken underwater, where there is this magical world I think to find something or someone. There is another creature that takes them there.

That's all I remember, I hope someone can help

Thanks.

Two creatures are taken underwater
By a third to find something

Vague description.

Here's a much earlier cartoon
From Famous Studios

Land of the Lost (48)

view

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It might also be Water Babies, a live action/animated film from the 70s.