Six Flags, in Houston it's the Children's Museum and the Arboretum & Nature Center, in Basel it is without a doubt the ZOO.
If you don't already belong to your local Zoo, you should. Join today. Our children love to play outdoors and right now and much of the year we don't have a yard so my solution is the Zoo. The Basel Zoo has a family of peacocks that roam freely through out the Zoo. They have two entrances and are within walking distance from downtown and near three tram lines and four bus lines. At the Zoo, go see the baby rinio, pet the goats, and see the new primate exhibit. Pack a lunch, stay all afternoon and look out for us, we're probably there.