great are Sol, the center of Madrid, for kids better go to La Casa de Campo, metro batan or take the cable car=teleferico at parque del oeste, there is an aquarius, zoo, and amusement rides park there. the metro will take you quickly.
all info about other parks is in the above link
the covered palace of xanadu is great too, a commercial center with skating ring,and cinemas, etc
Then it depends what specifics you want to do with the kids, Madrid has it all
Zoo is great place for families to have a day out and there is lots of entertainment designed for the kids, for example dolphine shows. But it is very interesting for adults as well due to wide range of animals, including panda, gorillas, elephant and hippoes.
If I go away with my friend I have to visit the local zoo!. Located in the Casa de Campo this zoo has over 2000 animals including snakes and tigers. It also has sharks in the aquarium. The park has been relandscaped which makes it fairly attractive as zoos go. I did feel that some of the areas that the animals were housed in were quite small.
There are plenty of places to eat, drink and rest those tired feet.
Entrance was 13.50 Euros in January 2005.
Here you can see all kinds of animals. There are 2.000 species, and a dolphinarium with regular shows, an aquarium which includes sharks, pavilions dedicated to venomous snakes and the 'mysteries of nature', as well as childrens zoo and parrot show.
You can also borrow some small 'cars' so that you do not need to walk on your feet around the whole park. Or why not a little boat?!
They also got some nice shows during the day with birds and other animals.