The most obvious answer is the Science Park.

There is a large science museum with lots of fun hands on activities.
There is normally some temporary exhibitions which are very good for children.

In the last few years there have been exhibitions on dinosaurs, arctic explorers, predators, automatons etc.
All of them are also designed to be interesting for children.

The birds of prey display is absolutely brilliant.
The falcons fly up into the air and then swoop down just over your heads to catch the meat being twirled around by the experts. You can see the owls up close.

The web site is here.
http://www.parqueciencias.com/eng/

From June until mid September there are many swimming pools.
There is a water park called Aquaola.

There is information about that and swimming pools here
http://granadamap.com/sport/waterpark.htm