We just came back from a field trip with our daughter's school there and had a great time! I am a little tired and didn't get to go on a number of rides because of my too obvious 8 1/2 months pregnant belly but I would definitely recommend a day trip there.
They have a section with miniature monuments in Taiwan and China, a Chinese arts performance then you ride their little train to the amusement park section. Most rides are ok for children taller than 90cm.
Here is the url: http://www.woc.com.tw It took us a little over an hour to get there in a big tour bus. I think it's pretty close to Hsinchu.
The Egyptian water ride is cool...but the weather's a bit too chilly for it now. My twins (they were just over 1 at the time) loved seeing the space shuttle and Jilong harbor miniatures in action.
Michelle, last time I went to Xiao Ren Guo I took a charter bus from the terminal near Taipei Station. You might also be able to get transportation through one of those weekend bus trip agents like eztravel.
A friend told me that there is a bus that goes directly there
and you take in close to Hsin-Yi and Dun-Hua.
There is also a bus that goes directly to Leofoo Theme Park
If you plan to go and need detail I'll check with her.