I've coached elementary kids in cross country and track, and we've always made it a point to do something fun as part of each practice. We wanted them to enjoy running and being part of a team. We always talked about improvement instead of performance, so always try to improve on your last race or run longer than you did last practice. Not everybody is fast, but with a little bit of effort, everybody can improve.
Specifically for cross country .... You will likely have a wide range of abilities, and we always set a goal of running (i.e. no walk breaks) the entire race. Some might take until the end of the season, some might never get there. We took the same approach with practice where we tried to get everyone able to cover a mile (short walk breaks allowed) before the first race. That was usually pretty easy, and we typically got up to 2 miles before the first race. By the end of the season, most could cover 3 miles (our longest), but some very slow and some with walk breaks.
We had a similar setup with 2 or 3 practices per week. One was always distance day where we would run roads near the school (close to college campus). We had parents run with us so we could have pace groups of 3-5 kids. Often we would mix in some fun stuff like follow the leader or fun routes or stop to look for turtles in the creek, etc.
Second practice was drills and/or hills. Pairs or teams work well for these and help build camaraderie. Short sprints, form, jumping plyos, tag, capture the flag, race the coach, etc.
Third practice if we didn't race was shorter distance run and a running game of some sort.
At this age, praise and encouragement are key! Criticism doesn't work. We talked about things we can improve, but always in a positive light. Encourage kids to encourage each other. Don't be a hard a$$, have fun with them.
My philosophy is that the slow and awkward kids need you more than the fast, athletic ones do. Give them confidence, help them learn and grow.