Ahhh, that brings back memories.
As a kid, my family was not all that well off (they're doin better now), and I wasn't allowed to have any pets. Well, when I was around 5 or 6, my parents caved in and let me get two goldfish.
I was so happy. They were a far cry from a dog, but still... they were something, and they were mine.
I named them "capitain hook" and "Mrs. hook", hahaha. They had a nice tiny fishbowl to live in, and I thought they were the coolest things in the world for the first day or two.
Then, the unthinkable. My little sister (2 years younger than me) decided she'd feed them. And oh, the humanity. Her 3 or 4 year old mind decided that they should eat what she liked... popcorn and koolaid.
Needless to say, after 2 or 3 days of sheer bliss, I lost my goldfish.
I never got a pet after that, only could keep whatever I could catch down in Louisiana. Lots of crawdads, snakes, spiders, minnows, etc... but no more goldfish. ::sigh::
If you really want to off them, drop a hint to your kids that the fish would like some of their favorite treats.