How are they under a false name? Don't you have to show ID and your Medicare card to get admitted?? At least, to get admitted without a hefty bill?
If there is any risk of the child being exposed to harm I would absolutely report it. Anonymously if needed.
I believe though that any of my friends would have already reported it him/herself as there's no way they would leave a baby (let alone their niece/nephew/relative of whatever degree) in a dangerous situation - and so I wouldn't need to be concerned that it might hurt my friendship anyway.

