With regards to the pet tube, you cannot get that until after you drink the potion, which unlocks the spell wheel.

As far as the potion is concerned, I have the PS3 version of the game, and I have noticed that my characters have the annoying habit of backing up a step or two when I walk up to a cauldron, which makes the cauldron menu / button disappear.  The solution I use is to slowly walk towards the cauldron and wait a second or two before pressing the button, to ensure that the character is not going to move.  That solution may or may not work for you on the Wii.