the first time my grandsons came to my house they were 1 and 3 years old (they live in AL, I'm in CA). the older one thought that my fish were the neatest thing he'd ever seen and he LOVED watching them (it was kinda lost on Bob, and still is at 5 years old). he banged on the glass once.. i told him that it hurts the fish and he immediately quit and asked what he could do. so i gave him a spray bottle of vinegar and water and showed him how to clean the front of the tanks. and when it was time to feed the fish i let him help me cut up the fish and shrimp and throw it in for the peacock bass..
Michael (7 now) still loves fish as much as i do, me and him had a blast at the Georgia Aquarium two years ago. And he still talks about coming to see my fish here in CA.