For places close to Dublin for just one night we tend to go to Skerries, Annagassan and Carlingford. Nice pubs and restaurants in all 3 and all beside the sea, nice walks, space for the kids etc. Haven't tried overnighting in Malahide or Greystones yet but have read good reports here. Rooskey is another good spot with full services (EHU, water, cassette toilet facilities).