It’s often the case that we don’t know as much as we think we do. Research is best done to find everything there could be instead of confirming what we think we know.
Family tradition indicated that a relative and her husband had three children. No mention was made of other children and their obituaries both indicated that they had four children. A search of birth records for the entire duration of their marriage located a first child who died shortly after birth. No mention was ever made of this first child. Such situations were not uncommon. Many families, for one understandable reason or another, did not mention children that died at birth or shortly after birth. These individuals can easily be overlooked if we only look for the ones that we know about.
That concept of “searching for everything, not just to find we already know,” applies to genealogical research in general–not just children whose short life may be too painful for relatives to mention.