Are you making up the bottles or is mom sending them ready? Make sure if mom is sending them that she is making them up properly and not watering down the formula because the child drinks so much. The result will be the extra water is not satisfying so you are in effect feeding half a serving of milk with each bottle potentially.
But anytime between 4-6 months it is ok to start cereals so I would be asking mom if that is ok and then do it mid morning at daycare to see if that holds child over better or at least reduced by one or more bottles.