Depends on the age of the child. If the child is over the age of reason 7, they would have to go for catechesis before joining the church…and at that point the child would be involved in the discussion I am sure. And of course, with them getting married sacramentally, and they have biological children, the Catholic spouse would be expected to do everything to raise the child Catholic. The non-Catholic spouse should be made aware of those vows, but is not expected to sign a document likewise.
In all mixed marriages, permission for a mixed marriage must be requested. The parish priest will assist in this simple procedure. To obtain permission, the Catholic party will be asked to affirm in some way (verbally or in writing) that he or she will do all in his/her power to see that the children of the marriage are baptized and educated in the Catholic faith. The other partner is to be informed of these promises and responsibilities; the non-Catholic partner may feel a similar obligation because of his/her own Christian commitment. No formal written or oral promise is required of the non-Catholic partner. In carrying out this duty of transmitting the Catholic faith to the children, the Catholic parent will do so with respect for the religious freedom and conscience of the other parent and with due regard for the unity and permanence of the marriage and for the maintenance of the communion of the family. It is important that during the marriage preparation, both partners together discuss the Catholic baptism and education of the children they will have, and, where possible, come to a decision on this question before marriage (The Ecumenical Directory, 150).