Small babies passes, a sticky, dark green stool called meconium soon after birth. This will continue several times a day for the first 2 days.
Then the stools change to a yellow colour and have a sweetish kind of smell. The baby passes a stool after every feed. This is absolutely normal, and should not be Called diarrhoea.
Some babies, on the other hand pass a stool every second or even third day and that too gets the mothers worried. This too is perfectly normal as long as the stool is not hard and the baby has no discomfort while passing it. Around 3 to 4 months the stools become less in number and the baby may pass one stool at almost the same time every day.
There will be a great difference in the stool of a breast-fed and a bottle-fed baby. The stools of a breast-fed baby are bright yellow, semi-formed, with very little smell, while stools of a bottle-fed baby are harder, darker in colour, and more smelly. Sometime they may be whitish also.
All this is normal. As long as the baby is happy and gaining in weight there is nothing to worry.