Procedure: Eligible mother-infant dyads will be contacted prior to routine 2, 6, 12 and 18 month clinic visits where during these visits, infants will undergo an immunization and naturalistic observations will be recorded. Coders blinded to the study will score pain intensity and maternal comforting behavior using validated measures. At the 18 month visit, trained medical assessors blind to group assignment will perform the primary outcome measure, Bayley Scales of Infant Development (3rd ed) (BSID-III).