Baby Talk
To be fair, this is not a hugely popular theme. However, it hits the concept precisely, through cloying voice work and appropriately-scolding library staff. Some people will find it sweet (especially the singing parts), but this is probably best as a short-term, "variety" theme.
To install the theme, please choose from one of the files linked below. Then follow the directions on the instructions page.
You may also want to check out the Baby Talk credits page.
An example of the "best of" theme:
Baby Talk Theme video (in MP4) (Converted AVI)