To a puppy, a baby is a totally different creature than a child or adult. The baby has a different scent and doesn’t look, move or sound like an adult to the puppy. It will take more time for the puppy to adjust to a baby.
Let the puppy smell a piece of the baby’s clothing or a blanket before the two meet. At their first meeting, the puppy and baby should be kept 10 to 15 feet apart, and brought closer very gradually, a foot at a time.
Keep a watchful eye and use careful judgment in deciding when the puppy is allowed to sniff the baby directly. Don’t leave the puppy and baby unattended together, even for a moment.
Most puppies adjust to babies easily, but some may not.