In Fl someone can be Backer Acted for a period of 72 hours then they are released unless they find there is something wrong. If he was backer acted someone felt he was a danger to himself or others and are seeking help for him that he might not have wanted. If under the age of 18 he has no choice in the matter, if over 18 he had a choice. <br />
If like you say he has been then he is under 18 which means his parents felt he was a danger to himself or others or had another reason to get him help perhaps they felt he would not. He will be released in 3 days they can't hold him unless like I said they find they have cause.
Remember that if in that 72 hrs, a certified psychiatrist does find cause for mental instability, he may be committed for a much longer time period.