It's not enough that they "had any children". For example, if they had exactly one child, and that child was childless, then they are not your ancestor.

Biologists define the "identical ancestor point" to be the most recent time X in the past such that every person alive at time X is either an ancestor of everyone alive today, or of no-one alive today. Computer simulations suggest that the identical ancestor point is quite recent in geological terms, e.g., it's probably within the past few thousand years (it would be even more recent if we ignored remote places like Tanzania). See: Rohde et al (2004), "Modelling the recent common ancestry of all living humans", Nature. https://www.math.arizona.edu/~bhallmark/TMRCA/naturerohde.pd...