We love watching movies in our house!  We took the kids to see Journey to the Center of the Earth which was rated PG.  Recently the wife and I watched Welcome Home, Roscoe Jenkins and it was rated PG-13.  Big difference between PG and PG-13 in these two!  The Center of the Earth movie was great for the kids but the Roscoe one I wouldn't take them to see until they were about ready to move out of the house!

It's hard to tell these days what PG, PG-13, or R stands for.  Here is the real site (MPAA) behind the movie ratings, I believe.  Some shows rated PG-13 have been ok for my kids but some are certainly not.  I have used a few sites over the last year or so when I wanted to know why a particular movie got the rating it received.  Two that I've used recently are Kids-In-Mind.com and CommonSenseMedia.org.  Both of these sites give you a lot more information than just the rating.  They give you an actual age rating and some actual detail as to how it got it's rating.