When a child neglects a pet (instead of a litter box) have a consequence ready.
Perhaps the other siblings can be paid to do the neglected chore out of the delinquent child’s allowance.
Maybe TV and gaming privileges are lost for a week.
Maybe the kid has to do extra chores to compensate for Mom taking over the task.
But there has to be consequences.
These pet care consequences have worked well for me and our family zoo, and hopefully they'll inspire you to modify them as needed or create your own.
Try the Tom Sawyer fence approach for pet care consequences.
Make pet care look like fun. Make walking the dog or brushing the cat seem like a privilege they have to earn.
This really does work in households with with several siblings sharing an animal.
Instead of issuing threats or whining, help kids come up with solutions. Sometimes they cannot care for a pet because they have band practice or they’re going to camp.
Fill in or let them hire a sibling. If siblings have their own pets, maybe they could switch off.
Try to make it their problem, but do help them work out a solution.
And if their solution is you, help them figure out how they can make it up to you. Work it out like a trade of labor. Wash your car, perhaps? Do the day's load of laundry?
Your call, but make sure they do make it up to you or pretty soon, you'll be the only one caring for the animal.
And that's probably not why you agreed to bring the pet home.
Don't make giving up the pet a consequence of not caring for it. You're only teaching her that animals are dispensable. Do you want her to get rid of you later on when she loses interest?
Pets, once acquired, are part of the family unless someone develops pet allergies or other medical condition or the animal starts biting. Pets are a serious commitment for the whole family.
And learning that love requires commitment, care, and sacrifices, is probably one of the best life lessons you can share with your child. And it all starts with enforcing pet care consequence.