15 month old dislikes formula.

Jed

Our 15 month old daughter has just started to learn how to chew and swallow solid food. She's still a bit picky. Now she's rejecting her formula. She used to be on mixed--breastfeed and formula. Now she just prefers the breastmilk. We can only feed her formula if she is really sleepy. Is this a normal phase for weaning? Shall we force the formula?