IMO what you are doing is great! I do the same thing. They do not get paid for it, but nor do they ever complain about it if asked to do something. Only I bath and brush her, but my oldest three (13, 10,7) fill her bowl with food and water. They also take her out to potty. These things aren't asked of them daily, I still do most of it myself, but they are definately involved.
It is a valuable thing to teach them about responsibility of being a pet owner. To me, it helps teach them that there is more to having a pet than just petting it and looking at how cute they are. They are another member of the family and of equal importance to me. They are just as dependant on you as a human child for their needs. My daughter goes to the vet appts. She has wanted to be a veterinarian since she was 4 yrs old. She has her mind made up and is focused, grades and all!
