Sometimes you will find a birth or baptism record for a child, but the parents already have a child by that name. Chances are the first child died as an infant or youngster and the parents named a subsequent child using the same name. This was probably a way of honoring the first child. You will most likely find a death record for the first child before the second child’s birth.
It was quite common for our German ancestors to call their children by their middle names. In the same family, several children could have the same first name, such as Anna or Maria, or Johann. These children were known and called by their middle names. See for example my fifth great-grandparents, Peter and Christina Marx. They had four daughters having Anna as a first name: Anna Maria, Anna Margaretha, Anna Catharina, and Anna Gertrude.