Were they drinking out of a bottle or a dish when you got them and are you sure the ball in the sipper is light enough for them to move? I've had some foster rats that did not know how to use the bottle but after putting a little bit of baby food on the sipper, they were quick enough to figure it out.

Mice don't come out of the womb knowing how to use a water bottle, they have to be taught by watching another mouse or by a human showing them; doesn't make them stupid.