FWIW:
The American Academy of Pediatrics currently recommends that "breastfeeding continue for at least 12 months, and thereafter for as long as mutually desired." * The World Health Organization and UNICEF recommend that babies be breastfed for at least two years.
Breastfeeding a toddler helps with the child's ability to mature. Although some experts say a toddler who is not weaned will have difficulty becoming independent, it's usually the fearful, clingy children that have been pushed into situations requiring too much independence too soon. A breastfeeding toddler is having his dependency needs met. The closeness and availability of the mother through breastfeeding is one of the best ways to help toddlers grow emotionally.
Breastfeeding can help a toddler understand discipline as well. Discipline is teaching a child about what is right and good, not punishment for normal toddler behavior. To help a toddler with discipline, he needs to feel good about himself and his world. Breastfeeding helps a toddler feel good about himself, because his needs are being met.
Just as babies do, toddlers receive health benefits from breastfeeding. Your milk continues to provide immunities and vitamins, and can help protect your toddler from illness and allergies. If your toddler does get sick, nursing will help comfort him. In fact, a toddler with an upset stomach may be able to tolerate nothing but human milk.
Toddlers have a huge world to explore, and breastfeeding provides them (and their mothers!) with some quiet time in their busy, waking hours.
A mother and her baby should breastfeed for as long as they wish to breastfeed. The American Academy of Pediatrics currently (2005) recommends: "Pediatricians and parents should be aware that exclusive breastfeeding is sufficient to support optimal growth and development for approximately the first 6 months of life and provides continuing protection against diarrhea and respiratory tract infection. Breastfeeding should be continued for at least the first year of life and beyond for as long as mutually desired by mother and child." * As solids are introduced, usually around the middle of the first year, your baby will shift his primary source of nutrition from your milk to other foods.
All the benefits of human milk--including nutritional and health--continue for as long as your baby receives your milk. In fact, as your baby takes less human milk, these advantages are condensed into what milk is produced. Many of the health benefits of human milk are dose related, that is, the longer the baby receives human milk, the greater are the benefits.
BUT -- I doubt I will BF DD#3 until she starts school--just not for me.