i dont think theres a deffinitive answer to your question, i dont know.
it all depends on your feeding schedule and what you feed.
from my experience, your bp will grow faster if its on rats compared to mice. ive also heard that bps of the same age will be larger if fed on rats compared to ones fed on mice.

you say you have a 2 month year old baby :?: :?:
i guess its 2 months? what are you feeding it?