Child-friendly things to do in Dublin? Now?

[NotQuiteCockney]

We are leaving for Dublin tomorrow. DS1 is 5.5, DS2 is 2.5. They're both pretty typical boys, love guns, trains, dinosaurs, etc etc. Oh, and farms are popular.

We're staying near St Stephen's Green.

Any outing suggestions?

A trip on the Luas? - the new tram type of thing....
There is a zoo in Phoenix Park but I've heard it's got a bit run down lately....

Lots of beaches within easy reach of the city centre.

St Stephens Green itself is nice.

There is one of those city tours you can do where the vehicle they use goes in the water as well (might be called Viking tours...)