Adam Clarke on Numbers 26:11

The children of Korah died not - It is difficult to reconcile this place with Num 16:27, Num 16:31-33, where it seems to be intimated that not only the men, but the wives, and the sons, and the little ones of Korah, Dathan, and Abiram, were swallowed up by the earthquake; see especially Num 16:27, collated with Num 16:33. But the text here expressly says, The children of Korah died not; and on a close inspection of Num 16:27, we shall find that the sons and the little ones of Dathan and Abiram alone are mentioned. So they gat up from the tabernacle of Korah, Dathan, and Abiram, on every side: and Dathan and Abiram came out - and their wives, and their sons, and their little ones. Here is no mention of the children of Korah, they therefore escaped, while it appears those of Dathan and Abiram perished with their fathers. See the note on Num 16:30.