One must not confuse parental input and the child's output. Babies will learn, it it just that they are not able to give the output (ability to show or speak) that the parents are looking for.
So I would like to think that from birth, it is the downloading in process stage. This is where the parents construct knowledge for the children.
The output stage will be at different age for different children. So parents, don't be disappointed if your children cannot give immediate output. They are learning. Give them time to show you. Once the knowledge has been constructed, when the child comes across what has been taught previously, it activate their prior knowledge or schema.
For example, I have expose my children to many different vocabulary from a young age. Sometimes, I'm not sure if they have absorbed all that I have taught. But there was once when my daughter Natalie(age 4 then) was watching a cartoon and she said "they must be in Japan" and I asked her how did she know and her reply was that she recognized the Tokyo Tower at the background. The amazing thing, I showed her the image of the Tokyo Tower long ago and she remembers.
So from Age 0-3: Start downloading.
In fact, children's ability to learn and absorb is very strong until age 3. Learning is almost effortless on the part of the child before age 3.