As with all of my ballet students, I like to get them turning -- just plain turning first -- before trying pirouettes. It's a great way to build up to what we think of as a simple pirouette. In the center, how about having them try waltz and/or balancé turns.
Here's just one example, which I do in Pointe class, but works well in regular class.
1) Facing the barre, make piqué sous-sus (either by making relevé from 5th position or by stepping to the barre from attitude à terre, aka, B+).
2) Make sur-le-cou-de-pied.
3) Make passé.
4) Make a promenade en de hors (yes, you'll have to reach around yourself).
5) Come back to sous-sus.
6) Return to either 5th position or to attitude à terre. (If attitude à terre, then I have students take a step back, going through 4th position, finishing some distance away from the barre. This makes them really have to work and use their muscles and some effort to get to the barre. Teaches moving/traveling, and it *feels* like your moving/traveling, too! And you can challenge them to now only move but to use their feet well, by working through them, placing them and turning them out, with the weight over the balls of the feet.)
Start with holds at each step (passé -- hold, hold; promenade -- hold, hold). Repeat left. And then after a while, have them repeat it en de dans.
Another great one to do at the barre, is to have them do piqué turns while still facing the barre and traveling de côte (sideways). In other words, they'll be travelling down the barre. A classic combination is: 3 with no turn and 1 with a turn. Passé is behind the knee, spot is to the barre. All with holds or "stays" at first. (Piqué 1, hold 2-4. Then build to piqué 1, hold 2.)
Have turn simple barre combinations or with specific exercises like: tendu back (inside leg), make a fouetté, turning in the direction of the tendu foot, close 5th, hold. Repeat left.
Or have them *just* turn from side to side, without even getting fancy with terms like soutenu or even on relevé. Have them try, if their right foot is front, just turning quickly left toward the barre and have them finish w/the left foot in front (pivot left, pivot right). Seems simple, yes?
You could also try something fun like have them do the plié combination this way: first position (R & L); second position (R & L); etc.
In center, try rond de jambes à terre with 1/4 turn for each RDJ, using either the walls or corners for the completing point of each. Eventually, have them try this en de *dans.*
For barre and/or center: parallel passés and then promenade them. Parallel at first, then turned out.
Hope some of this helps! I suggest being creative but always try to tell your adult students WHY you're having them try something. It helps them understand better what it is you're trying to get them to do and give them a measurable goal. Best wishes for happy teaching!