Dr. Greene's Answer
As long as your child is in diapers, every single poop will be right there for you to see when the diaper is changed. During these years, the stools undergo several changes. The first poops are the thick, sticky, tarry meconium stools that consist partly of old skin cells that are shed and then swallowed while the baby is still inside you. During the first week these give way, in breast-fed babies, to soft, yellow, breast-milk stools. These usually look like yellow mustard with little seeds. By the time a baby is one week old, he has an average of 8 to 10 of these pleasant (as stools go) stools each day.
For most breast-fed babies, the number drops to about 4 per day by 4 weeks old (although many kids have a different pattern). Formula-fed babies usually stool less often at this age, and the stools do not change much with time until solid foods are introduced (because unlike breast milk, formula doesn’t change over time). Formula-fed stools are often tan or yellow at this stage, and a little firmer than breast-milk stools. For any baby, tan, yellow, green, or brown stools can all be normal.
By 8 weeks old, the average drops to 1 per day. Most formula-fed babies will not go less often than daily, but many breast-fed kids will poop even less often than this. I know many babies who only go every three days. If a happy formula-fed baby goes 4 days, or a breast-fed baby goes 7 days without a stool, I recommend that he or she be checked once by a pediatrician (sooner if the child seems to be in pain). Still, it can be completely normal to go only once every eight days — as long as the stool is soft when it comes out. Breast milk is an amazing food that leaves very little in the way of waste.