Kids will love it.Castle park is beautful ,(as is the Castle.)theres a great playground in the park.
There are some great little cafes for a nice lunch.
The shoppings pretty cool too.great quirky shops.Try go to kitlers (pub) there they tell the story of the witch,the kids will either love it or hate it!!Theres a tourist office off the high street and you will get load of information there,and maybe buy the " kilkenny People" newspaper to see whats happening locally.Enjoy.