Our pedi told us to make sure we did give them some formula in sippy cups. Some kids who only get to practice on water or juice don't quite get it that they are supposed to drink milk/formula out of sippies too. They fixate on the fact that milk comes only from bottles and don't want to drink it from sippies.

I used to give my kids formula and then milk in sippies right after their meal at the normal bottle time. I figured if they were thirsty they would be more willing to try. I did not expect them to drink much since it was just for practice. I would then pour the rest of the formula/milk in to bottles. Once I knew all 3 kids were capable of drinking out of sippies we switched.

Lori

http://yesidohavemyhandsfull.blogspot.com/