I tend to look for common situations with a lot of variations. Get the kids messing with something first, and
then start feeding them solutions. It's very easy to remember the solution to a problem you actually have, but before you experience the problem the solution is basically just arbitrary information.
One thing I introduce right away is the freestyle situation of shot-and-bodylock. Put one kid in on a double, on his knees, and have the other kid lock over the top on his chest. From there, the game is easy: if the defensive man rolls you, he wins. If not, you win. As they get the hang of it, you can show them how only one guy can get his butt under his head, and that's the guy who's probably going to win. And you can point out solutions to individuals, like releasing with one hand and posting to prevent the roll. Mix it up by changing to a high crotch, letting the offensive man start on one knee instead of two, giving the defensive man a crotch life rather than a top body lock, etc.
Another routine I use I extrapolated from something Sergei Beloglazov said about an aspect of his training growing up. Give one of the kids a high single, and then let them work from there: the offensive man needs to get the takedown to win. As the kids get used to the game, start pointing out differences between the positions and solutions they can use. For instance, the defensive man's compromised foot can be inside, between the legs, or outside; the offensive man can lock his hands, wrap on the leg with one hand over and the other hand under, put both hands under, hold at the knee or at the ankle, the defensive man can take a whissor, etc. I try to balance the tips I give: give the offensive man ways to finish from the different positions, and the defensive man ways to escape or compromise the offensive man's advantage.
Similar situation: chest-to-chest, on the knees, arms over and under. Try to put the opponent on his back, without stepping up. Variations: let them step up with one foot or the other, but not both at once; lock hands and keep them locked; one man has double under; start more or less side-to-side, where one man's underhook becomes a seatbelt, etc.
None of these require any experience, and kids don't question how they got into these situations, so you can just run with them. You can make any of these a regular part of practice, and not exhaust the possibilites for a long time. In fact, they'll probably push you to improve as a coach; these are suprisingly complex positions, and you may well realize that you don't actually have solutions to some of the problems you see. The high single practice, particularly, improves balance and fits into a warmup routine well. Of course, switching sides should be part of all of these.
Along a similar line, there's a nice game I call "shoelaces", where the kids score points by trying to untie each others' shoelaces (no double-knotting). A better version of this is available as
Attack Bandz, though buying them for a lot of kids would get pricey.
It's fairly easy to come up with other ideas for situations to explore like this; just watch wrestling matches. Actually studying the situations, so that you can teach strategies and solutions, is where the work is. But you certainly don't need to master a situation to get started with it (in fact, it's more the other way around).
Throw in some fun exercises like
square pushups, stunts like
circus rolls, and running-around games like
sharks and minnows, and change things as soon as you see the kids starting to get bored, or lose focus.