What also works great, if puppers isn't lactose intolerant,is a little bit of yoghurt mixed with a little low sodium chicken broth. (plain yoghurt). Put it in the Kong, and FREEZE it. You can freeze the PB, too. All day tongue workout for puppers. Whatever you do, stay away from the "Kong Stuffing" sold in the spray cans. It is basically meat flavored fat, and is really bad for the dog's digestion, not to mention horribly fattening and nutritionally useless.
The do make teensy Kongs. Stay away from ANY toy that only has one hole in it. Toys like this, even balls, that have holes in them, MUST have a hole at each end. If only one hole it is possible for the dog to get its tongue sucked into the toy and stuck, causing massive swelling, choking, and risk of tongue amputation.
For teething, soak a washcloth in chicken or beef
broth, wring it out and leave it tightly twisted. Freeze it. Give it to the pup frozen. Chewing it will feel good on sore gums, taste good, and help the new teeth break through. If you notice retained puppy teeth, haul to vet to get them removed. This is critically important in toy dogs as retained teeth (usually canines) can cause/worsen malocclusion; already a problem in the tiny tots.
Also, Kong does honor their guarantee as regards indestructibility. I've sent back a few of the supposedly indestructible huge black kongs after one of my GSDs destroyed them. I always got a new kong from the mfr. That said, the Kongs lasted those brutes longer than any other toys I'd gotten them.
You said you were starting on toothbrushing early, which is a good thing. Try using a chlorhexidine toothpaste if you are not. They're gum friendly and regular use will prevent the development of gum disease in most cases.
Best of luck, the only teeny dogs I've had were a yorkie/border terrier cross and a longhaired dachshund that I fostered. The yorkie x was an adult when I got him, and his mouth was already a mess. The dachsie was a half-grown pup and a real sweetheart. Couldn't get him house-trained, which apparently is an issue with the breed, but a sweet little guy. He had an awfully impressive set of teeth in that long little snout of his.