If you need something that's not entirely grown-up, but not kid-like either, try TrueTypefont Pijamas from designer Billy Argel.
Pijamas reminds me of the way I used to make 3D letters, before the idea of fixed point perspective took hold. The glyphs seem to rotate, which strangely work in a cute, naïve, tweenish way. Pijamas includes both upper and lowercase letters, plus common punctuation: comma, period, exclamation and question marks, the "at" sign and hash, and the ampersand to name a few. Designed as a display font, using Pijamas smaller than 24 points makes it look a little silly, but at much larger sizes it's relaxed and easygoing, with a tiny hint of growing up to be a wild-child.
Pijamas is free for personal use; for commercial use, contact Argel.
Note: To use this font, unzip the folder and install the .ttf file in the folder C:\Windows\Fonts. Note that the font won't appear in your applications until you close and re-open it. For more guidance see How to Install and Uninstall Fonts in Windows.