When children are taken to the hospital with injuries severe like this it's standard practice for the hospital to do an investigation, of sorts, into the matter to determine if the child is safe in their home.
I can't speak for everyone in the medical profession, but I have some family friends that are RNs that have told me several times that they're legally required by law to report to CPS/HS any activity that they suspect in regards to a child or an elderly person's wellbeing.
Basically the hospital has an obligation to discuss what happened to the child with the child, and then report it to the authorities if they think the child's wellbeing is in danger (You know, making sure mom and dad weren't doing this kind of thing).