Actual self weaning rarely occurs before the age of eighteen months. Disinterest in breastfeeding before that age is referred to as a nursing strike. There are ways to keep the baby at the breast because premature weaning is, indeed, a problem. The American Academy of Family Physicians advises mothers that a child weaned before the age of two is at increased risk of disease.

If you wish to avoid supplementation with formula, all you need to do is keep nursing four times per 24 hour period. If the baby nurses at least that much, you don't need any other kind of milk or milk substitute. It's ok if it only takes the baby five minutes to nurse, at that age they may be very efficient at taking milk from the breast.