I love Newport because I have a lot of family there, but aside from being a small town there isn't a great deal to do there for a young family. There is a quay that you can walk around and go across the old railway bridge. There's a famous butchers Kelly's with a tea room, they export sausages and black pudding internationally from this little shop.
Mulranny beach is nice for young kids which is half way to Achill, well worth stopping. The hotel just above the beach is a nice place to stop for
Lunch as well. There is Yvonne's tea room on the side of the Greenway which gets well recommended, and Nevin's pub is excellent with very good food, surprisingly good.
Above all the area is beautiful if you get the right weather. When in Mulranny there is a road that goes out to the sea channel and you often see pods of dolphins along there sheltering in from the Atlantic.