This article presents a comment on the article "Family Sizes of Children and Family Sizes of Women," by Samuel Preston, previously published in the journal "Demography." Preston has recently analyzed the historical relationship between the average family size of women and the average family size of their children in the U.S. The difference over time between the average number of children ever born to women and the sibship size of their children is due, of course, to changing proportions childless and to changes in the dispersion of number of children ever born. There are two reasons why this fundamental fact may be incorrect. First, Preston compared the family size of children of the depression to the family size of baby boom children by using data for women aged 45-49 in 1950 and 1970, respectively. However, since these women did not confine their childbearing to either the depression or the baby boom, the meaningfulness of Preston's comparison is obscured by reproductive noise from non-relevant time periods. A second, more severe, problem with his findings is that they do not take account of changes over time in pre-adult mortality.