The World Health Organization and UNICEF strongly encourage global breastfeeding through toddlerhood: “Breastmilk is an important source of energy and protein, and helps to protect against disease during the child's second year of life.”
Your milk is still providing your child with essential proteins, nutrients antibodies and other protective substances and will continue to do so for as long as you continue nursing. Human biology is geared to a weaning age of between 2 1/2 and 7 years (Dettwyler. K). “It takes between two and six years for a child's immune system to fully mature. Human milk continues to complement and boost the immune system for as long as it is offered” (La Leche League).
Extensive research on the relationship between cognitive achievement (IQ scores, grades in school) and breastfeeding has shown the greatest gains for those children breastfed the longest (van den Bogaard, C. et al), (NCT) .
At this age many children form attachments to comfort items. This reliance peaks during their second year (Encyclopaedia of Children's Health; Stringer. K). Examples include rags, toys, dummies and even a bottle, objects that can all be mislaid, forgotten or lost. The beauty of breastfeeding your toddler is that your child's source of comfort is permanently attached to you. Furthermore, nursing does not produce the harmful health consequences that a dummy or bottle would at this age (e.g. dental malformation, tooth decay, speech delay).