GIMP  http://www.gimp.org/   Free
Very good at converting between various graphics formats including from .PDF to .JPG

Tux Paint, A paint program designed for Children 3 and up. 
http://www.download.com/Tux-Paint/3000-2132_4-10328696.html?hhTest&tag=lst-1&cdlPid=10816165  I have looked at it but not tried it with kids.

Windows Movie Maker or Windows Live Movie Maker, you probably already have it.  Type movie in the search box or START > PROGRAMS  >  WINDOWS MOVIE MAKER in Windows XP. This program can shrink a movie file down so you can e-mail it or it can rotate the movie from Landscape to Portrait or clip parts away.  One problem is the only format it puts the files out in is Windows Movie Video, WMV which is a Microsoft developed format and Apple computers can not read it without adding extra software.  Another confusing item is when you go to save a movie, you have the option of saving the PROJECT or the MOVIE.  Select the movie or no one will be able to play it.

Sound Editing

Video Editing

Windows Live Movie Maker, free from Microsoft, will only output files as .WMV files.  The big advantage of this program is that you can rotate the image so you can rotate a landscape image to portrait.  I am so used to doing this with pictures that I get caught when I take a movie and if it fits better in Portrait, I just shoot it that way then have trouble displaying it.  When you go to save the file  (the icon one in from the right side) use the drop down menu to pick the size of the image, it defaults to a huge size.  640 by 480 ("For my Computer) is usually adequate and is a lot bigger than Facebook displays.  You can load bigger files to Facebook, they will automatically cut it down to size.

Edit digital Videos with Avidemux, http://www.download.com/Avidemux/3000-13631_4-10829933.html?hhTest&tag=lst-1&cdlPid=10857009 Have not tried.