Question about grammar in folk tale「ももたろう」

My question regards the use of 「だけ」in this story. Here are the three lines with the translations that were provided:

ももたろう は まんま を 一(いっ)ぱい たべたら 一ぱい だけ、
If Momotarou ate one cup of rice he grew one cup,

二(に)はい たべたら 二はい だけ
if he ate two cups he grew two cups and

ずんずん 大(おお)きく なって、
quickly became large

The first and second lines of translation say he “grew;” is this an implication of the third line? 「だけ」implies that something equal to ぱい た occurs, but the lines them self do not state growth from what I understand. Am I missing something?

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This will be definition 2 - “as much as; to the extent of”. And yeah, “grew” is implied by the third line.

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Thanks a ton.