No doubt you'll do what i did pippa. My eldest when younger did exactly the same, pottered home with a goldfish from the fair. I went mental and swore under my breath all the way up to the petshop for a bowl (I didnt know then they are better in a tank), bought the bowl, food, gravel, silly novelty toy, spent a bloody fortune and the damned thing died that night!
Since then, I researched em a bit, and now I have a tank in kitchen with 2 goldies (one's a black moor) massive one in living room with tropicals in and small one in bedroom with a Siamese fighter in.