The area around Drury St, George's St, Powerscourt townhouse has nice independent shops and lots of cafes.
Avoca on Suffolk St is lovely and has a good cafe, traybakes etc
Trinity is nice to walk through, book of Kells etc
Not many bookshops left, Hidges Figgis is the biggest, nice cafes nearby.
Collins Barracks museum is on the red Luas (tram line) has the decorative arts, the Kildare St museum has more archeology and artifacts. Natural history museum is very charming and next door the National Gallery is world class.
Be careful about opening hours that week though, a lot of places are closed for the week between Christmas and new year.
You could take the DART ( local train) out to Greystones, the scenery along the coast is lovely and the village is cute. If you like walking there's a scenic walk to the next town Bray which is very popular. Then get the train back into town, you could stop off in Monkstown which is full of restaurants and cafes.
Funderland is a funfair that's only on after Christmas, very popular although I haven't been for a long time but your girls might enjoy it.