If you have ever watched "Alvin and the Chipmunk", you'll find that the songs sung by the chipmunks was very different in pitch. Actually, you can also apply Chipmunk sound effect to a song as long as you have a audio editing program that comes with pitch editing. That means, by adjusting the pitch of the song, you will have Chipmunk singing effect.
Well, you'll probably start thinking about such program. Where can we get such program to do this kind of audio editing. There's a free program where you can download free to do this task. It's Expstudio Audio Editor. You need to install the program first before using it. After installing it, you need to open a song i.e. mp3 song. Then, select part of the song or press Ctrl + A to select the whole song.
After selecting the song, you click SpecialFX menu, then click the effect you desired. Try selecting Chipmunk. By using this program, you can also produce female voice songs from male voice songs, or male voice songs from female voice songs as well.