Only start attending classes with baby at about 2, 3 months. A baby’s filtration system only develops at about 8 – 10 weeks. For this reason, some experts say human babies need the first three months of life to give their brain and central nervous system the time needed to mature. Breathing starts to regulate and begin to soothe herself. This time between birth and the end of a baby’s third month is a unique stage of life that many now refer to as the “fourth trimester.”Babies of this age get far too stimulated