The fact that the children of Dasan and Aviram stayed with their father was enough to include them in the sin. The children of Korach did teshuvah and moved away from their father so they were saved. In fact Hashem replies to the entreaties of Moshe.
"Speak to the congregation saying, 'Withdraw from the dwelling of Korah, Dathan and Abiram.'"
This leads to:
So they withdrew from around the dwelling of Korah, Dathan, and Abiram, and Dathan and Abiram went out standing upright at the entrance of their tents together with their wives, their children, and their infants.
This implies that the children of Korach did withdraw from around their fathers tent and did teshuvah.
Note that the infants are in the position of being killed by their parents like someone refusing to leave a burning building or evacuate during a flood. and not allowing the children to be saved. The adult children of Dasan and Aviram could have left with the infants.
As Rashi says on that pasuk.
their wives, their children, and their infants: Come and see the severity of dispute. The earthly courts do not punish until [an accused] has two [pubic] hairs, and the heavenly court does not punish until one reaches the age of twenty, but here even nursing babes were punished. - [Midrash Tanchuma Korach 3]
The implication is that even those who could not of their own free will leave, were caught up in the punishment, even though they had not done anything themselves.