I like relay races for young kids...so they barely even notice they are conditioning. Also they don't have to count, which is good because at that age some of them can't keep track. We do stuff like...
-crab walks
-inchworm walks (stand up, touch your toes, walk out to plank, push up, walk toes in to hands, repeat)
-bear walks with straight legs
-sideways log rolls (for abs), try to keep your feet and hands off the ground
-wheelbarrow with a partner
-frog jumps
-koala walks under the beam or bars - they basically hug the beam from beneath and hold on while they shuffle down the beam
-monkey walks on bars - chin up position, try to shuffle down the bar with the chin staying up
-leg lift walks on bars - hold an L shape, shuffle hands down the bar while keeping feet above the floor or an object
They also really like climbing the rope for some reason, which is handy.
I'd imagine they'd like plyo stuff too - obstacle course where they have to jump over a bunch of stuff, do some kind of conditioning exercise at the end.