If you want something good for the kids, then a community tank is perfect. Mollies, Platys, Guppies, some colourful tetra's (neon, scissortail, head and tail lights) and maybe some goby's would fill a ciclid tank with colour.
They are relatively friendly, and guppies, mollies and platys are all live-bearers, meaning that they give birth to live young, giving the kids something to keep track of and watch as they grow.
They are also quite cheap to buy and keep, so if there are any casualties, you haven't lost as much as if you bought yourself an expensive fish like a black knife ghost or Discus or something.
Good luck...