My beautiful bitch is 2yrs old and it was her 1st litter and she ended up having 9 puppies, they seemed fine and within 24hrs one by one started dying. My kids and I are devastated Over this loss. Vet said since she carried so many they didn’t develop right. I feel so empty and heart broken from this horrible experience. It is so hard to explain to my kids what happened.

So sorry for your loss.  It sounds like fading puppy syndrome, this is often caused by the canine herpes virus. Many breeders in the UK vaccinate against herpes during the pregnancy.

So sad to read about this - have you lost the entire litter?    If so, mum must be physically and emotionally in trouble and at least need help to scatter her milk.

https://vcahospitals.com/know-your-pet/puppy-fading-puppy-syndrome-in-dogs

This is what this sounds like although for sure 9 puppies for a Dachsie would, I suggest, be a very large litter indeed.   Not that this has to happen however!!

There are many websites with a ton of info. about what this might have been.