It is a cliche, but Tiovoli Gardens really is an all ages attraction.
For adults it is a pleasant (if perhaps overly manicured) garden/park with pleasent walks, shows and many restaraunts.
For children it is a fun park complete with roller coasters, ferris wheels, and side show games.
The rides tend towards the tame though (there are no triple loop roller coasters, and the mood is more of a garden/park with amusement attractions than of a genuine fun park.
The entry fee is quite cheap, and rides are extra. Food is not inexpensive but is not much more expensive than outside the park.
There are usually at least two free shows a day.