K.S.
When my son started eating more solids; cereal, fruits, veggies, etc... he did stop drinking quite so much milk/formula. We were fairly relaxed about his feeding schedule and tried to let him grow into different amounts as necessary. I think a good rule of thumb is to monitor his/her weight gain/loss and worry accordingly. Our Pedi. did not seem to worry about the slow down on milk/formula as long as he was still hitting his growth/development milestones.
Check with your Pedi.
Hope this helps...