I don't think that pets and children can really be compared as they have little in common other than both need to be cared for to some degree. In general, pet's medical, food, and education( if they need disobedience training) are WAY WAY WAY less expensive. Pets bring comfort, children take comfort away. Pets bring peace and tranquility, kyds take that away. Most pets, especially cats, can be left for days at a time as long as they have a clean box, and plenty of fresh food and water, kyds HAVE to have 24/7 supervision which means they have to go along, or care has to be arranged and often costs money.
EVEN IF you have to have someone come check on a pet, let him out, feed him, etc.....it's not nearly the time consuming job as it would be to find a sitter, so a critter sitter is easier to procure than a kyd handler. If he has to be boarded, it's not NEARLY as expensive as "boarding" a kyd and the kennel doesn't expect a favor in return like a friend or relative would. Pets make messes, but not on the consistent and extreme basis as a kyd. Pets are glad to see you when you come home and greet you with kisses and kitty head butts, whereas a kyd is angry that you did anything which didn't inlude them and demand a toy or a new dvd to make up for it.
Pets don't get knocked up unless you allow it, have freaky friends with skin heads and swastika tattoos, nor do they have to have squealing little friends over for a sleep over and then proceed to destroy your house and your sleep. Pets don't hog up bathrooms, borrow clothes and makeup, and take the keys to your car and then wreck it. Pets don't have mandatory PTA meetings, talent shows, ballgames and other boring things you are expected to waste time attending. They also don't have to be driven to piano practice, art lessons, and soccer practice 3 days a week. Pets don't bring home shitty report cards and then have to be carted BACK and forth to summer school every day to make up for their laziness during the school year.
Pets don't rebel and say they hate you and that they love their "real" moomie better, even though they haven't seen her in 3 months. Pets don't take money out of your wallet, use your credit cards, and wear your new pajamas before you can. Pets don't expect an 8 course meal every night and tell you "there is no food in the house", if you don't have any easily made microwave pizzas, popcorn, chips or other junk food on hand. Pets don't have Dominoes pizza on speed dial and your credit card number on file and charge up more pizza in a month than a house payment.
Pets don't expect anything, but they get very happy when they get attention and love and little special treats from time to time. Pets are SO much better than chyldren, that I find it difficult to compare my pets to them. While an elderly pet may be inconvenient or require more care for a short time, that's MILD in comparison to the time and energy it would take to be a caregiver for a fucked up kid who had to be taken care of 24/7 for possibly it's ENTIRE life. It seems that most kyds who have to be cared for like this by a parent ALWAYS have the happy news delivered by a doctor of, "Well, sure he won't ever walk, crawl, piss or shit on his own, be able to roll over or say much more than goooooooo gaaaaaaaa, or hold his own head up, but the GOOD news is he should live a long and normal lifespan, with proper care of course.
I think that pets are better than kyds, so I guess my opinion is biased.