I grew up in St Fintan's, and my parents still live there. It was a very nice place to grow up. With the sea on your doorstep and the hill just up the road there were plenty of amenities to keep us kids amused.
There are plenty of sports clubs (golf, sailing, tennis, rugby etc.) in the area. The nearest shops are at Sutton Cross, the local newsagent having shut up shop a long time ago.
While there were a lot of kids around 15 to 20 years ago or more, I see very few these days on my occasional visits. House prices which are out of reach to most young families has seen to that.
Some of the local bus services have been downgraded in recent years, due to lack of demand I imagine. The 31A route used to travel right through St Fintan's 4 or 5 times a day, but it has been withdrawn completely now. The 31B and 31C routes serve Carrickbrack Road, which is about a 10 minute walk, while Sutton Cross and the Dart station are about a mile away.
I don't know what the traffic situation is like at Sutton Cross these days, but it wasn't too bad many moons ago. The main roads to the city centre all lead into Fairview and North Strand though, which seem to be pretty bad in the mornings. Parking used to be a problem at the Dart station, but again I don't know what the situation is like now.
All in all, a great place to bring up children if you can afford it.