The first issue of the new Shazaam for kids is great. Anything Mike Kunkel (who's the writer and artist for it) is just great for kids. Herobear and The Kid was a blast. I havent checked out any of his other stuff, but it all looks like a load of fun for kids.
I gave my kids my Carl Barks Library (the hardcover B&W ones) when my daughter turned 4. She loves Uncle Scrooge, Gyro, et al. I also buy her the Don Rosa Uncle Scrooge books from Gemstone. Both kids love Franklin Richards: Son of a Genius. I'm getting them the Bone color editions and Jeff Smith's SHAZAM next....
Well it sounds whorey but I also think it's a valid suggestion. My own book Minister Jade is pretty kid friendly. It's not technically a kids book, but it's not inappropriate for kids either, and youngins seem to enjoy the colorful art.
DC has a new line of comics called Minx; comics for girls. There are some really good stories (and a couple that are a tad dull, but to each his own). They've just started their second season of releases, but I've only collected the first season so far. My favourites are Kimmie 66, Confessions of a Blabbermouth, Good as Lily, and The Plain Janes. Check out the library here: http://www.dccomics.com/minx/
i loved as a kid (but i was al little older than 4) f.e. Prince Valiant, Yoko Tsuno, Lucky Luke and Spirou and Fantasio but it helped that they were available at the local public library