I'd go with your instincts here. A youth or children's advocate sounds fine in this context.

2008 and Earlier - Repeal 43 » Newswww.repeal43.org › news-2008-and-earlier
... and neglect, the New Brunswick legislature unanimously passed a law in 2004 providing for the creation of a **children's advocate.** The position is still not filled.

PA Child Ombudsman Public Hearing 6-19-18 - Scribdwww.scribd.com › document › PA-Child-Ombudsman-Pu...
Jun 19, 2018 - An Ombudsman would be in the position to do a neutral. investigation of a case ... support of the creation of a **Children's Advocate**. When I was ...

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Note added at 1 hr (2020-07-08 14:00:19 GMT)
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Even with the additional context provided in Discussion, I'd stick with 'advocate' if a natural-sounding text (that fits) is a priority. The use of 'protector' here would result in a foreignizing effect. In the end, advocates speak-up on behalf of others. In doing so, are they not defending them?

Although some people may be reluctant to choose this (and I must admit it's always sounded a bit weird to me), the Wikipedia description seems to fit and also offers several synonyms:

"A children's ombudsman, children's commissioner, youth commissioner, child advocate, children's commission, youth ombudsman or equivalent body is a public authority in various countries charged with the protection and promotion of the rights of children and young people, either in society at large, or in specific categories such as children in contact with the care system. "

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Note added at 2 hrs (2020-07-08 14:20:13 GMT)
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I think a stronger term than just "advocate" is needed here, especially if it's to stop bullying and paedophilia...

dirección_general_de deportes
"Se encarga de planificar, proyectar y construir o en su caso mejorar las instalaciones deportivas propias del consejo y la administración y gestión del patrimonio del mismo; promover e impulsar la mejora en el rendimiento y resultados de los deportistas mediante la realización de pruebas, estudios e investigaciones científicas y tecnológicas; asesorar a las federaciones; promover la educación física y la práctica del deporte; desarrollar la normativa que pernite el igual acceso al deporte de personas con discapacidad y fomentar la igualidad de género, sexo, raza o cualquier otra en el deporte y elaborar y proponer resoluciones de recursos o reclamaciones interpuestas ante el Consejo Superior de Deportes..."
"It's responsible for planning projects and building better sport facilities owned by the council and town management, aiming to promote and activate performance improvement with results by means of assessment, scientific and technological studies and investigations to advise the federations and organisations, as well as promoting physical education and sport facilities. This develops the ethos which allows open access to sport facilities reaching an equality which includes those less able or with less physical stamina. It must increase equality among young people regardless of gender, race, age and ethnicity in sport. It aims to propose resolutions on resources or claims imposed before the superior council on sport with a general code of conduct (regulations) reports, agreements, legal instruments of collaboration and administrative procedures."