Do cats adopt kittens?

I gotta question. My grand mom has these cats that's outside, it's a mom,daughter, and she had two kittens but one died. The kittens are like 3weeks old. Well today my grand mom went out and seen another kitten.. Why did she bring the other ones around and just bringing this one around? Anyone know?? Do cats adopt stray kittens?

They can do it, surely. Not the common but can surely happen.  Especielly if one of her own died, so she has place for another one to adopt.

Cats in home do often adopt if humans come with a new be.  Dogs may do it too.  Outside its not as frequent, but it happens yes.