In normal situations, both. The right that parents have to represent the children (in proceedings, signing contracts, contracts, etc.) is the right of “parental authority”. And both parents have it, by the mere fact of being their parents.
The fact that the parents are separated does not deprive either of them of the right of parental authority. Even if only one of them has custody. Because the fact of not having custody, does not mean that the parental rights have also been lost.
The parental authority is only lost by an express judicial decision. In which the judge has assessed very serious conduct of the parent in question, justifying the removal of parental rights (violence, endangering the life of the child, etc.).
A case that I will not forget, which made me see the importance of parental authority being exercised by both parents: I was representing a minor, in an appeal that he filed for a matter related to his education. I filed a writ requesting certified copies, which was only signed by the mother. The court told me “no”, because the representation of the minor is held by both mom and dad. Therefore, the letter should have been signed by both of them.
Of course, the above could admit exceptions. In case there is some extraordinary case, in virtue of which it is not materially possible for the 2 parents to represent the minor. In such situation, considering the specific case, the Judge could allow only one of the parents to represent the minor. For the sake of the best interest of the child.
