I'm so sorry for you and your family and that poor puppy. My little one has been sick since we picked her up on 12/28. I have just about $700 in vet bills to date and still counting. I was lucky in that the lady she originated from is issuing a full refund back on her to pay for the $$ already spent on vet bills as well as her continuing vet bills. We are just waiting for an agreement to be drawn up.
I feel so badly for your and your children. PLEASE INVESTIGATE should you decide to buy another. Adoption is another alternative. You can try
Pet adoption: Want a dog or cat? Adopt a pet on Petfinder and look for a Yorkie through rescue. I would also go for a bigger yorkie since your children are young. I know when we got our first Yorkie, we asked for the biggest in the litter. Our boys were young. Our Newman as an adult was a sturdy 12 lbs. full grown and brough my boys and our family so much joy. We had him 11 years before losing him to cancer. The upside about adoption through rescue is you know what you are getting. The dog or pup is already vetted and they won't lie to you about conditions or temperment etc. Plus they are spay or neutered already if old enough and if not you are usually eligible for a spay or neuter certificate which is also a great savings.
Again, I'm very sorry for you and your family.
Elaine