There are many synonyms for the phrase "natural children," which refers to children born to two biological parents. Some common alternatives include "biological children," "born children," "legitimate children," "own flesh and blood," and "genetic offspring." These terms emphasize the biological connection between the parents and their offspring. However, it's worth noting that using the phrase "natural children" can sometimes imply that children born through assisted reproductive technologies or adoption are somehow less valid or "unnatural." Therefore, it's important to be mindful and sensitive to the diversity of ways families can be formed, and to consider using more inclusive language such as "all children" or "my children".