Immigrants and their descendants increasingly shape fertility patterns in European societies. While childbearing among immigrants is well explored, less is known with respect to their descendants. Using Swedish register data, we studied differences in fertility outcomes between first- and second-generation individuals in Sweden and compared with the native Swedish population. We studied men and women separately, distinguished between high- and low-fertility backgrounds, and differentiated whether the descendants of immigrants were offspring from endogamous or exogamous relationships. For most migrants who arrived in Sweden as adults, we found elevated first birth rates shortly after arrival. First birth rates among the second generation were generally close to but lower than the rates observed among native Swedes. Male offspring from exogamous unions with a Swedish-born mother tended to have less depressed rates of first birth than other second-generation individuals. Second birth rates were very similar across population subgroups but generally lower among immigrants and their descendants compared to native Swedes. Third birth rates were often polarized into high- and low-fertility backgrounds, when compared to native Swedes. While fertility patterns among the second generation appeared to drift away from patterns of the first generation, the second generation remained a heterogeneous population subgroup. Nevertheless, and as childbearing patterns of the descendants with one immigrant parent increasingly resembled patterns of native Swedes, exogamous partnerships can likely be considered an important factor behind this gradual family-demographic assimilation process.