Research into regretting childlessness:
"Among the voluntarily childless women, all but one reported either no current child-related regrets, or regret that was 'minor,' 'fleeting,' or 'more of a curiosity than a regret.' Almost all reported no change or less regret with age, or that they were even more convinced that their decision to remain childless was the right decision."
"There are no group differences in the number of general regrets between mothers, voluntarily childless or involuntarily childless women. This indicates that regrets about childlessness are not especially salient among the involuntarily childless women, as they are no more likely to spontaneously mention them in response to a question about general regret. It is only when asked specifically about child-related regrets that significant group differences emerge... Research on the psychological consequences of childlessness must take into account the total life experiences of individuals."
Sherryl Jeffries and Candace Konnert, "Regret and Psychological Well-Being Among Voluntarily and Involuntarily Childless Women and Mothers," International Journal of Aging and Human Development 54, no. 2 (2002): 89-106.