@ Zabuza-lov-haku
No Worries! I'm glad to hear it wasn't my translation that was confusing.
I think the granny was checking Nagisa's body for telltale signs of having gone through the rigors of childbirth (stretchmarks, sagging, breats, that sort of thing). Nagisa's body still looked perky and pristine so Granny decided that she had never given birth and the kids aren't really hers.
Honestly though, I think the scene was actually an excuse to show Nagisa getting her boobs grabbed...