Maybe you should try the stage 3 nipples, with the largest openings? The stage 2 might not be big enough, and cutting a hole does make it too big (my husband did this once and it also drowned our baby!!). I never tried adding cereal to formula, but that's the only way I could imagine it passing through the nipple and not just blocking it. My other suggestion would be to mix it up as well as you can before even putting it in the bottle to avoid lumps in the formula from the cereal. I hope this helped! You might also call the pediatrician if all else fails and ask what they tell moms to do who have had to mix cereal with formula in terms of the bottle, the best kind, etc. I'm sure you're not the only mom to go through this. Good luck and keep us posted!