If you do not want to spend a fortune, yet want to have a great day out if the weather is good, here are a few ideas you should consider when planning where to go:
Playground, Pet farm, Fisheries, Rose garden, Cycle track, Allotments, Sports & playing pitches
Playgrounds, Walking Paths, Coffee Shop, Farmer's Market, Cycle Paths, Fairy Tree, Miniature railway, Walled garden
Playgrounds, Visitor Centre, Cafe, Walled Garden, Tea Room, Bicycle Hire, Road Train, Aras An Uachtarain, Farmleigh and a lot more to see
Playgound, Rose Garden, Walled Garden, Cafe, Playing pithces, Food Market, Road Train, Woodland walks, Cycle Paths. If you have the time, Dollymount beach is a must visit, too.
5) Sandymount to Poolbeg Lighthouse Walk ( including Irishtown Nature Walk)
Gorgeous walk from Sandymount Strand to the lighthouse
"An oasis of calm and beauty" that offers regular events for kids and adults alike. Its cafe sells wonderful coffee and scone.
Glendalough is the "honeypot" of the Wicklow Mountain National Park, so it is a must visit each year
http://www.wicklowmountainsnationalpark.ie/VisitingGlendalough.html
8) Bray - Greystones cliff walk
Wonderful walk, might be combined with eating an ice cream at Gino's, strolling on the promenade & spending some time on the new playground (Plus if it starts to rain, Sealife is always there...)
Wonderful walk, might be combined with eating in one of the restaurants Howth offers and visiting the Museum of Vintage Radio or the National Transport Museum
Playground, cafe, lovely view of the Dublin Bay
Have Fun!