Polish people are generally very friendly and patient with children; so travelling, even with small kids, is easy here.

There are numerous activities to be done with children and you can find a non-exhaustive list at the following website: http://www.cracow-life.com/poland/kra...

On a rainy and cold day, you can visit the Aquarium http://aquarium-krakow.com/en/ that opened in 2008 and contains a nice assortment of species. It will keep you and your little ones occupied for a good 2 hours in a warm and friendly environment.

Polands largest water park http://www.parkwodny.pl/eng/index.php . 2,5 km notheast of the Old Town. Bus 125, 128, 152 from the train station. 

Park Jordana http://www.cracowonline.com/334-Jorda...             Several activities for children of all ages. Some free. Renting boats and cycles , playgrounds and fast food. 

http://www.kryspinow.com.pl/  in polish only. Between airport and town. Kryspinow Beach is sandy beaches situated along an artificial lake. A small fee to enter. Facilities : snackbar, restaurant, toilets. Bus 209, 269 to Kryspinow Zalewem bus 239, 249 Kryspinow.