@Duainfey
when I was translating it, I tried googling it but couldn't find anything, and only thing I found close was from an old thread on yahoo
asking "バインバインって何ですか?" or "What is Bayin bayin", so I took the answer he got there.
it does make sense for it to be boob related tho
she wanted to eat a lot and grow
EDIT:
I checked with Miko the Manga TL and it seems like you're right, it does mean a big rack.
Fixed it