My 9 year old begged for a dog, and we finally caved a few months ago. He promised to help with feeding and cleaning up hairs and such. He loves her, no doubt about that, but the work has definitely fallen on me. Sometimes it feels like more of a chore than a joy for him (and for me). Was I naive thinking a 9YO would actually keep this promise? Now that we’re in it, how do we make sure the experience is positive for both the pet and the kid, and us?
we got a puppy when my daughter was 10, and the “I promise to take care of her” phase lasted about three weeks before the novelty wore off. 
we had to break tasks into kid sized responsibilities. For example, my daughter fills the water bowl every day and takes the dog out for a short walk after school. I still handle the bigger stuff like grooming, but giving her small, manageable tasks has made a huge difference. It’s still work, but at least I’m not doing everything! Maybe you could try something similar?
I hear you. We’re in the same boat, except it’s with a guinea pig, who knew such a small creature could require so much upkeep?! My son was so excited at first, but now I feel like the one managing all the cage cleaning, food, and playtime. It’s hard because I want him to learn responsibility, but I also don’t want the animal to suffer. Honestly, it’s exhausting. Sometimes, I wonder if we bit off more than we can chew. I don’t have any answers, but I just want to say you’re not alone in this!
You’re not alone in this, it’s super common for kids to lose interest when they realize how much work pets are. But the good news is that it can be a positive experience! Maybe set up a pet chore chart and tie it to rewards. For example, if your son helps with feeding and grooming consistently for a week, he gets to choose the family movie or dessert that weekend. It’s a fun way to keep him engaged and teach responsibility without it feeling like a punishment. Hang in there, it gets better!
LOL, this is taking me back to when we got a cat. My daughter swore she’d do “everyyyyything”. Then reality hit. Now the cat’s basically my pet, and she gets to swoop in for the cuddles. I joke that I’m the unpaid staff, and she’s just here for emotional support! 
But really we’ve made a deal where she does one chore for the cat every weekend. It’s small, but at least she’s still involved.