Selenia, Beta and the Bee
Near the end of the film, only Beta and Selenia are still minimoys and they are riding a bee. We see a scene where they discover another bottle of "Minimoy Maximizing Liquid" and ask the bee to open the cap. After this scene, I don't remember exactly what happened to our two heroes, but later in the film, I'm pretty sure they are not taller than they were.
So why didn't the liquid work on them ?