I went back in 1999 to see Paco Pena, before it expanded (I think they have a water park and hotels there now that weren't there when I was), and absolutely loved it!
It's divided into different lands, and the theming's really detailed, quite similar to Disney and much nicer than I'd expected. The rides were a lot of fun, although I don't remember there being a lot for smaller children.
I'd definatley recommend visiting it!