Good programming takes time to develop, it's not just a matter of grabbing some DVDs off the shelf.
What to show on the channel, anyway? Is there a theme? Consider specific programming for kids between about 7am and 10am. +++Need more here+++
Once you decide what to show, in order to make a schedule you need to get accurate times (Total Run Time or TRT). This means hours, minutes, and seconds (and frames if you're really being picky); "89 minutes" from the DVD case won't do. A good tool for this is http://www.videolan.org/ VideoLan, which runs on just about any common platform. Be aware that not all distributions have correct times in the metadata, exercise some sense when using these times (if you know the movie is 89 minutes and the reported time is 10, you've got a problem). If you're planning to get content off of non-digital media, transfer/ingest the content first then get the time.
The convention will need licenses for everything to be shown. Usually a single blanket license will do for all motion pictures, cartoons, etc, however even the blanket licenses do not cover every bit of content out there (for instance, they usually don't cover anime). Stills that are created by the convention won't be a problem. Conventions should have an ASCAP/BMI license for incidental music and to cover a masquerade, and this will also cover whatever music is used on the channel as filler.
Life will be much easier if all of the intended content is already in digital form. If you must pull content off analog tape, plan for at least double it's run time to get set up and to make a good copy. Likewise, you need to start with good media and be prepared for some things not to cooperate. It may become necessary to abandon some content because you can't get it off the media (see Ingest +++ for more info).
When there's time to fill between major items, consider filling with a mix of shorts, trailers, cartoons, and stills. It isn't necessary to put all of these on the published schedule, except maybe the cartoons.
Sets of stills should definitely be included in the overall programming. These can include programming announcements, general info (e.g. art show hours), random facts, etc. The stills should have a consistent format. Groups should be assembled to fit the holes in the schedule (see below). Usually music will be played when stills are shown, if none is selected at this stage, the engineers will select something. (Generally, instrumental works of limited dynamic range work the best.)
Make 640x480 jpeg or png, 24-bit color, leave a 5-10 pixel blank border around the edge (same color as the background). Don't use super thin lines, really complex fonts, or busy images; the transmission will actually loose maybe 30% of the detail. To check, take a slide and downsample by maybe 30% (to about 450 wide), if that's still readable, it's probably OK. Badge art can make a nice background, if there's enough blank space for text.
If you really want to be correct, make the images 720x480 with rectangular pixels (10:11), otherwise, don't worry about it.