I am loving the look of the fabulous Free Activity Trails in Dublin for Families on the Ingenious Ireland website. These free PDF walking trails with a geeky twist are suitable for ages 6 plus. There are three different Dubl1n by Numb3rs Trails which include counting, measuring and calculating activities to help kids discover the world of algebra, shapes and spaces. Each trail takes 60-90 minutes. Each pack includes a map and full instructions.
There is also a Dublin Metropolis Trail which aims to encourage kids to discover how the city works and the things around us are engineered.
There are guided tours too which have got great reviews on Tripadvisor but these might be aimed more at adults.