Hi, I dont live in Mt Gambier, but we go there a few times a year as my DH races motorbikes and they have a road race track there (Mac Park).
So from my experience as a visitor, it's a lovely place to go with kids. Some great playgrounds; beach less than half hour away (Port MacDonnell); lots of shopping - a long main street full of all kinds of shops, plus couple of shopping centres, including a new one being built with a Big W and specialty shops; great public swimming pool (we spent nearly 5 hrs there on New Years Day because it was stinking hot at the racetrack and we were camping in a caravan so no way to keep cool); good playcafe; lots of local markets; excellent library which has recently been done up. Fairly flat around the main part of the town, so good for walking with prams and kids.
The only experience of the hospital I've had was a few years ago when DH came off his bike and injured his finger and had to go to emergency. He had no complaints and was treated fairly quickly, but no idea about the maternity - or even if they DO have maternity???
I think I recall that there is a member or two I've seen on here that live down that way, maybe by me replying it might bump up and catch someone else's attention.