I was told by my local vet to use Adams flea and tick repellant spray on my chihuahua who was nursing 3 week old babies. I was told to use a rag and spray it, wiping it on her back only and to do the same for my 3 week old babies, citing that they use it all the time there with no ill effects. I did as I was told and was losing my pups one by oneand told that I must've done something wrong or its something else. I put a call into Alameda East in Denver and spoke to a vet there. They told me to bathe momma and do not allow her to nurse the remaining pups. I have lost all but one of my six babies.

I would never use any flea treatments on 3 week old puppies.
Although I am unfamiliar with Adams products as far as I know none of them are safe at that age.

The vet in Denver gave you the right advice. For fleas on very young puppies I recommend just bathing them weekly in dish soap, same with the mom.
Clean all bedding and vacuum your carpets regularly.
The dish soap drowns the fleas but unfortunately it doesn't kill the eggs which is why bathing weekly is needed until they are old enough for a proper spot on flea treatment.