Beweleys Ballsbridge have reduced their family rooms to 99 per night. It's in a good location and is clean and family friendly and you can pop over to the Four Seasons for a bit of glamour.
Jury's Inn at Christchurch is very handy for the centre of town, has family rooms afaik. Basic but not very expensive, and very central. they also have one in Parnell Street and one on the quays near Sherriff Street. www.jurysinns.com
i always stay in cassidys hotel its one minute walk from the spire, very limited car parking only i think 10 spaces, ideal for shopping includes an all you can eat breakfast buffet,