I asked my 21-year old daughter (who is in college but home for the holidays) this question, and she answered in a smart-aleck fashion (I just don't know WHERE she gets that from). She actually adopted a nasal, little-boy voice (she's a theater major) and started singing, "I want a Hippopatamus For Christmas". I slapped my knee and said, "Okay, but you have to sing the vocals." She agreed, and this is the result. I didn't really try for the carnival sound, but liked it when I heard it, so it stayed.
Edit: Oooops, I forgot the formalities... my apologies. Most of the sounds here are GPO... except for the drums, of course. I also use RealGuitar to echo the melody line, but it's swallowed up by the organ and you can't really hear it. Also, the MIDI was aranged by Ron Tilden, and I acquired it at the following website: http://www.xmasfun.com/Lyrics.asp?ID=89