Despite progress toward gender parity, women remain underrepresented in academia, particularly in senior research positions. This study investigates the role of parenthood in shaping gender disparities in academic careers, focusing on the complex interplay between gender, childcare responsibilities, gender role beliefs, institutional support, and scientists' career achievements. Using a large-scale survey of 5,670 U.S. and Canadian academics, supplemented with bibliometric data from Web of Science, it reveals that childcare responsibilities significantly mediate gender disparities in both subjective and objective academic achievements, with women assuming a disproportionate share of childcare duties. In particular, women shoulder a greater caregiving load when their partners are employed full-time outside academia. However, egalitarian gender role beliefs have been playing an important role in shifting this structure by transforming women academics' behaviors. As women's egalitarian gender role beliefs strengthen, their childcare responsibilities tend to diminish-an effect not mirrored in men. Institutional parental support policies show mixed effects. While flexible work schedules and childcare support can mitigate the negative association between childcare responsibilities and career outcomes of women academics, policies such as tenure clock extensions and paternity leave may inadvertently intensify it. Addressing these disparities necessitates a comprehensive approach that integrates shifts in individual attitudes, broader sociocultural changes, and policy improvements.