There seems to be much variance between preschool teachers at our gym- ranging from the "serious" focus on learning names of skills, correct form etc to the more fun. Also, I can think of a bunch of catchy tunes to sing to the warm up exercises rather than just counting to 10.... yes or no??
You can absolutely have fun with them, use your imagination, etc. For warm-ups I've seen our coaches play games (a mat is a pirate ship they have to get on), instead of just running laps to get the blood pumping. They have contests, who can do the most sit ups, pull ups, leg lifts, v-ups (this is pre-team, so you can adjust to whatever you're working on). It just makes it a little more fun then "Do ten push ups". It sounds like you got the kid thing down pat, and once you get gymnastic fever it's over. ;-)