Everyone's pretty well covered it. Nothing is out of the norm with your friend. It is common for fertility to return around the 14-15 month mark and many mothers seem to choose (or not) an age gap of about 2 years with their children. The hormones of pregnancy generally reduce the milk supply for the older baby. This poses no problem for the breastfeeding toddler as he/she can make up the shortfall easily from other foods (and does not need formula, of course) and they are still getting "some" breastmilk in addition to their solid diet. Most toddlers continue to breastfeed (many mothers take this opportunity to wean, but if a baby is still welcome at the breast they will usually keep feeding - not in every case, but most cases) Then, when the baby is born, obviously milk supply flourishes and many mothers find that continuing to feed the older child eases the adjustment of having another baby in the house for the older child.