Infants are dear to my heart. By tenderly responding to their unhappy sounds, we teach them that they can trust their adults to meet their needs. This is so important. I carried my babies in a baby carrier in front whenever my hands were needed for other activities. I will do the same for yours.
At the same time, I recognize the need for babies to have "tummy time," so they can learn to creep and then to crawl. These are important developmental stages that increase brain cross-over communication.
Also, I believe that infants become better learners when their adults echo their first attempts at communication (cooing and burbling), respond with them and tell them what they are seeing, hearing, and feeling. My daughter was three when a professor of psychology said she had the vocabulary of a five year old. I have seen studies that document, "some children begin school with twice the vocabulary of others. These differences can be traced all the way through Elementary School in reading scores."
Finally, I am reading a great book on an extensive sleep study of infants. The 90-Minute Baby Sleep Program is teaching me more about meeting infants' sleep needs. I would recommend this book. http://www.pollymoore.com/