Are there any free/open fonts designed to help learn/read Chinese?
as Stumpy Joe Pete said, you'll be hard pressed to find a font that works in all cases, and that you may want to look into a browser extension that highlights, magnifies, and explains the character you've hovered over.

I recommend Pera Pera Kun: http://www.perapera.org/

They have extensions for FireFox and Chrome.

Here's a snapshot:



I have never seen or heard of a font that will provide that functionality intrinsically. Kids Chinese books, however, often have the pronunciation under the characters to help the kids learn.

Hope this helps.