Canon 34

If the parents, or the Catholic spouse in the case of a mixed

marriage, transfer to another Church sui iuris, children under

fourteen years old by the law itself are enrolled in the same

Church; if in a marriage of Catholics only one parent transfers

to another Church sui iuris, the children transfer only if both

parents consent. Upon completion of the fourteenth year of age,

the children can return to the original Church sui iuris.