If you are using OS X, the fastest way to backup is with DVDBackup (freeware),
DVD2oneX (about $55US) and Roxio's Toast Titanium ($89-99US).
1st: The DVD must be backed up to the hard drive using DVDbackup. If the kids
watch the movie on the computer there is no reason to go further. Apples' DVD
player can play the files saved to the hard drive (a larger hard drive may be
2nd: DVD2oneX takes the backup and compresses the movie down to fit on a
standard 4.3 GB blank DVD-r.
3rd: Toast Titanium is needed to burn the DVD files to a new blank disk.
Time varies depending on size of movie, amount of compression and burning speed
but doing it all steps at once expect about 2+ hours with 2x burn speed, about
3+ hours with 1x burn speeds.