My 11yo son and I will be in Dublin for a violin workshop this August and will have 3 free days after the conclusion of the program. We will have already seen much of Dublin and I would love advice from veterans on what we should do next! I am not a confident stick-shift driver, but also don't want to do the big tour bus thing either. I thought we could start by taking the train to Galway. His program ends on a Sunday afternoon, we have a flight home out of Dublin on Thursday at noon. All advice welcome!
Taking the train to Galway is probably a good idea since you only have three days. From Galway you can do some bus tours to the Cliffs of Moher, Aran islands, or Connemara region. Also, there is some great traditional music to be found in Galway. With so few days it's better to just pick on place and stay there as you will actually see more this way than constantly moving on. Google day trips from Galway to see what's available. You should be able to catch a train back to Dublin on Thursday morning and still get to the airport in plenty of time as I think the first train leaves at 0530.
You don't say when in August you'd be in Galway, but be aware the Galway Races are around the first week of August and draw a lot of people into the city in the evenings for drinking in the pubs and things can be a little rowdy or noisy depending where you are staying. Galway does make a decent base if you want to just take some small day trips via a tour bus - but if you hate that kind of thing, there is an option to just take a "tour bus" to one of the ferry ports for the Aran Islands (it's really just a ride to the boat), then you're basically boarding the ferry and when you get off on the main Island, it's very easy (and not expensive at all) to get a mini-van driver, pony & trap or bike rental to go around the island. I like staying on the Islands overnight, but aside from a couple pubs (which won't let kids in after a certain hour), there's probably little that would hold interest of an 11 year old once the sun goes down.
Another option besides Galway (if you want to avoid driving) is to leave Dublin and head to Northern Ireland via bus or train. You could do something along the lines of stay in the seaside town of Portrush on Sunday and Monday evening, see things like Giant's Causeway, Dunluce Castle ruins, walk across the rope bridge, etc. Then head back to Belfast early Tuesday morning and spend the day and night there and be back in Dublin for your final night before you head home Thursday.