It's not just children that people want photos of, animals are a very big part of some people's lives. The chance to have a professional portrait of a much-loved pet is something that a lot of people really appreciate.
I have sold vouchers for portrait sittings, including for a lovely lady's pair of dogs (no children involved!).There are some (but not too many!) differences to working with people, but the rewards are the same, when you capture something special about the pet for their owner to treasure for a long time to come.