Sexual assault is a catchall term. It covers everything from groping to anal rape. It is a little frustrating to not know the severity of these actions from this kid, but the reality is, it doesn't really matter. If he's this embolden to attack four women in broad daylight, there is every reason to think he could become more aggressive as he goes on. Most serial killers start by torturing animals, or doing petty theft. They escalated. Paul Bernardo was the Scarborough Rapist before he killed his sister-in-law or Kristen French/Leslie Mahaffy.
As someone else pointed out, think about the fact police released a photo of a minor to identify them. That shows how concerned they are. If they can get him help and prevent him from doing even worse, that is a very good thing.