For injury time out, the referee has lots of limits on what they ought to do in judging whether the time out is "legitimate". If the kid and/or coach requests an injury time out, then the referee is to grant it. We don't necessarily know why they need that time out - could be something we cannot observe (e.g., the kid feels they are about to vomit, or they need to take a hit on their inhaler for their asthma, etc.). It is unwise for a referee to deny a request for injury timeout and take a risk that the kid could be hurting badly.
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That being said, the rules book has always stated, "Taking an injury time-out for a non-injury situation is unethical." However, it doesn't prescribe a penalty for that. Common thinking among officials is that we would issue an Unsportsmanlike Conduct penalty if we judged that this type of unethical behavior had occurred. But, in a practical sense, there is little we can do to make that determination absent some very blatant actions or words by the "injured" contestant or coach.
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It's a tough situation, and the injury time-out can be abused so that a kid can catch a breather, or get a quick coaching clinic on something the opponent has been doing successfully, etc.