Honestly I would walk away from this breeder and look for a pup elsewhere. I know everyone is excited to get a puppy but you're asking for trouble. I would be terrified to leave a 7-9 week old puppy home alone for 4 -8 hours a day. Yorkie pups are tiny and need to be monitored to make sure they are eating, otherwise they can suffer from hypoglycemia which then can lead to seizures and death if not treated immediately. Pee and poop in the crate is the least of your worries at that age. Puppies need to go potty when they wake up, after they eat, after they play, and whenever they feel like it.
I brought my yorkie pup home at 13 weeks old and she weighed 1lb 15oz. I took off from work for 2 weeks to make sure she would be ok away from her mother and siblings at her size, to bond with her and get her on a feeding/potty schedule. I used a crate and an ex-pen for training with no potty pads. She didn't like to use them so i just took her outside from the very beginning. After the first 2 weeks I went back to work but would come home on my lunch hour to take her out, feed her, play with her, and then take her out again. So at 15 weeks she was able to hold it those 4 hours while i was away. That's double the age of the pup you want to bring home.
Do yourself and your children a big favor and do not buy from this "breeder". Go to
Yorkshire Terrier Club of America and look for breeders in your area. There are also threads here on YT with guidelines for buying a new puppy. There are several red flags to look for and letting puppies go before at least 10 weeks old is a big one. Puppies should stay with their mothers and siblings until 12 weeks old to learn social behaviors and manners.