@MyBusyUser The average 9 year old is not going to care in a meaningful way for a dog. She can't walk it independently. She can't really train it. She can't pay it's bills or take care of it. Best she can do is feed it.
FWIW, my DDs have just had their 'first' dog at 12 and 13 although honestly she's my dog - i'll be the one breeding her one day - but DDs love her and she sleeps with them, so for arguments sake she's 'theirs'.
But I would say they are absolutely not the 'average' children (they go to dog shows with me and have since they were toddlers, for example). Most of the 'hard' training is done by me still because most children are really just are not capable of having the authority to train a puppy (children get too excited and overstimulated etc). I foot all the 'mental' load that comes with pet ownership - making sure she has flea and wormer, making sure she's developing well, that her seasons don't take too much out of her, monitoring her for health issues or illnesses. And it's a lot.
Unlikely children, a dog never grows up. They're perpetual toddlers in terms of the time/energy you spend on them - just when they get older, it's like caring for an elderly relative.
But, if you do decide to go ahead, please consider the breed carefully - don't be taken in by designer mongrels and backyard breeders. Go for a healthy, stable, pedigree from a breeder who can match you to an appropriate dog and give you the aftercare/support you need. A poodle or a labrador would be a good choice as they're typically very stable in terms of temperament.