According to the book "How to choose and raise a puppy" as soon as the kids are a little stronger, you can try to determine their gender. To do this, place the puppy in a vertical position or flip belly up.
How to determine the sex of the dog
Inspect the crotch between the hind legs. The dog penis is almost on his tummy, and bitches it is located closer to the anus. In appearance of the sexual organ swirls reminiscent of a heart.
If there is any doubt, look at adult dogs. Babies are all the same. Determining the sex of newborn puppies, take the time to check the skin, ears, eyes, hair. If the eyes are watering, and my ears started up a tick, show the puppy to the vet immediately and start treatment.
How to determine the sex of the dog