All of humanity are 'children of Noah' by definition, so the question is really "are you an observant Noahide?" (i.e. one who is promised a share in the world to come).
One answer is that many religions and legal systems come very close to qualifying as living up to the Noahide standard, but fall short on a few areas. So by supplementing or reforming an existing faith, one may live up to the Noahide requirements. Some Rabbis are of the opinion that reforming and correcting existing national faiths is the highest form of Noahide.<ref>Rabbi Yosef Gikkitila, Rabbi Nathaniel ibn Fayumi, Rabbi Ovadiah Seforno, Rabbi Menachem Meiri, Rabbi Nachman of Breslov, Rabbi Yaakov Emden, Rabbi Henry Pereira Mendes, Rabbi Israel Lipschutz, Rabbi Elijah Benamozegh, Rabbi Samson Raphael Hirsch, Rabbi Abraham Isaac Kook, Rabbi Jonathan Sacks, Rabbi Adin Steinsaltz</ref> For example Aime Palliere, a Noahide taught by Rabbi [[Elijah Benamozegh]] remained a Roman Catholic and continued going to church (albeit with a modifed intepretation).<ref>"The Unknown Sanctuary" by Aime Palliere.</ref>
Alternatively, another approach is join with one of the many communities of Noahides worldwide. These communities are best for people who have fallen out with establish religion and wish to take on some of the Jewish customs. Some Rabbis are of the opinion existing religions are beyond repair, or that Noahides are forbidden from creating a religion. They feel that taking on a voluntary set of customs, untainted by idolatry, is the highest form of Noahide.<ref>Rabbi Shlomo ben Yitzhak (Rashi), Maimonides, Rabbi Yehudah ben Betzalel Loewe (Maharal), Rabbi Isaac Luria, Rabbi Menachem Mendel Schneersohn (Chabad), Rabbi Zevi Yehudah Kook, Rabbi Yoel Schwartz</ref>