Gendered terms being super vague or not existing in Japan always makes translating stuff like that into English really weird.
"この子" can have different meanings in Japanese. For instance, it can be used when a teenage boy sees a cute female model in a magazine and says, 'この子かわいいですね、めちゃタイプ.' and it's obvous that he means "this girl". It can also be used by a parent or an elder person when introducing their child to others, like 'この子は...'."
Sometimes, it can literally translate to "this kid", but not all the time.
The thing is that even though the phrase itself isn't inherently gendered, the speakers often still have a specific gender in mind when using it to refer to someone. In the end It's all up to the translator's interpretation based on context, since fan translations aren't official and usually lack a way to confirm these things with the author.