Short answer. Yes. The courts may appoint a guardian of the child's property, or a guardian ad litem, when the best interests of the child so require. Parental authority is the starting point, not an absolute bar — the child's interest is what the article makes decisive.
What the law says
The courts may appoint a guardian of the child's property or a guardian ad litem when the best interests of the child so requires.
Family Code, Article 222 — Guardian of the Child's Property; Guardian ad Litem. Read the full provision →
Two different offices in one sentence
A guardian of the child's property manages assets belonging to the child — an inheritance, insurance proceeds, land put in the child's name — and the office continues for as long as the appointment lasts. A guardian ad litem is appointed for a particular case, to represent the child's interest in that proceeding and nothing else. They answer different problems, and confusing them causes needless alarm: the appointment of a guardian ad litem in a case is not a finding that anything is wrong with the parents.
The standard, and what it is not
The only criterion the article states is the best interests of the child. It does not require proof that a parent is unfit, and it does not depend on parental authority having been suspended or terminated. That is a low threshold in form but a demanding one in substance, since the court is being asked to say what actually serves this child. Common occasions are a conflict between the parent's interest and the child's in the same property or the same case, and the sheer size or complexity of what the child owns.
It does not displace you as a parent
The appointment concerns property, or a case, and leaves the rest of parental authority where it was. You continue to have custody, to make the decisions of upbringing, and to owe the duties of a parent; what changes is who manages the identified assets or who speaks for the child in a proceeding. Parents commonly assume the two things travel together and read the petition as an attack on their standing. Read the order for its scope instead — that is where the answer to what you may still do actually lies.
If an appointment is proposed
Whether you are asking for one or resisting one, the case is made with facts about the child's situation rather than assertions about anyone's character. Assemble what the child owns and how it came to them, the records of how it has been managed, and the specific decision or proceeding that has prompted the question. If you are opposing, be ready to show that the child's interest is already being served. If a conflict of interest is the ground raised, address it directly, because it is the hardest one to answer by general assurances.