Hmm..well it helps if you are an adult sometimes...not always though lol. My folks like all my critters,well at least I think they do haha. Since they dont have to take care of them,its all good. I have a mini-zoo not including my fishies. I have now taken over all but two rooms in our place with fishies! I took over the kitchen counter much to my folks grumbling about it haha. We dont have much counter space to begin with,then I go put a fishy on it. Heh. I also moved my moms bread box to accomodate my new fish. Rearranged the living room so I could put my panda tank in there.
I think it helps if your folks like animals too bascially and know that you are taking care of them,without needing them for anything.