If parents have the US citizenship: Need not to apply for children A child who originates citizenship through a parent gets US citizenship automatically and need not apply to preserve US citizen status. There is a rule, when a person gets citizenship through a parent or "originates" nationality through a parent gets US citizenship automatically and need not file an application for citizenship status. Note that this rule is different from the rule that apply to a child born abroad to a parent who is already holding US nationality. Under this rule, a child derives US citizenship if they meet the three subsequent conditions: 1. One parent should be a US citizen by naturalization or by birth. 2. The child is not about 18 years and he/she is unmarried. 3. The child must be in the custody of citizen parent and residing in the US physically and legally.
Conversely, note that an "illegitimate" child cannot derive US nationality from a US father. The child can derive only if he/she is legitimated before turning in16 year . Under whichever set of rules, the order of events makes no difference. If he/she is a permanent resident and under 18, the child gets automatic US citizenship. If you believe you are an imitative US citizen, the best proof is a US passport. It expenses you less to get a US passport than a Certificate of Citizenship. Adding my experience, passport officials are more fair that the United States Citizenship and Immigration Services (USCIS) in deciding whether a person derived US citizenship.