This article put zero effort into explaining why the children were there in the first place, so I went looking.

Some teens escaped from the Bridge City Center for Youth and in response the Governor started sending children there. Same article:

DOC has identified a vacant building on the grounds of the Louisiana State Penitentiary that, with minor modifications, can house many of the juveniles currently at BCCY, while keeping them in separate facilities from adult inmates at all times.

I believe BCCY is juvie of no particular subtype, i.e. we can safely assume these kids committed some crime, but have no basis for speculating what sort of crime.