Candy, I modified your example code as follows, and cannot reproduce
the effect you're describing.  the parents and children are randomized
with respect to one another.  Keep in mind that for three children and
three parents, there are 6! = 720 possible shufflings, and of those 72
of them have all the parents and children grouped together.

Sean

---[uses]--------
public class Agent implements sim.engine.Steppable
        {
        public String str;
        public Agent(String s) { str = s; }
        public void step(sim.engine.SimState state)
         {
         System.out.println(str);
         }
        }
----------------

Using BeanShell I dumped in this:


import sim.engine.*;
Schedule schedule = new Schedule(2);
SimState state = new sim.app.heatbugs.HeatBugs(100);  // an arbitrary
SimState

for (int i=0;i<3;i++)
        schedule.scheduleRepeating(schedule.EPOCH,0,
                new Agent("parent " + i), 1);

Steppable reproduction = new Steppable()
        {
        public void step(SimState state)
                {
                for (int i=0;i<3;i++)
                        schedule.scheduleRepeating(schedule.time()+1,0,
                                new Agent("child " + i), 1);
                }
        };

schedule.scheduleRepeating(5,1,reproduction,5);


Here's what I got

bsh % bsh % schedule.step(state);
parent 1
parent 0
parent 2
<true>
bsh % schedule.step(state);
parent 0
parent 2
parent 1
<true>
bsh % schedule.step(state);
parent 1
parent 2
parent 0
<true>
bsh % schedule.step(state);
parent 0
parent 2
parent 1
<true>
bsh % schedule.step(state);
parent 1
parent 0
parent 2
<true>
bsh % schedule.step(state);
parent 0
parent 1
child 1
child 0
parent 2
child 2
<true>
bsh % schedule.step(state);
child 0
child 2
child 1
parent 1
parent 2
parent 0
<true>
bsh % schedule.step(state);
parent 2
child 1
parent 0
child 2
parent 1
child 0
<true>
bsh % schedule.step(state);
parent 1
child 2
parent 2
child 0
child 1
parent 0
<true>
bsh % schedule.step(state);
child 0
child 1
parent 0
child 2
parent 2
parent 1
<true>
bsh % schedule.step(state);
child 0
parent 0
parent 2
parent 1
child 0
child 1
child 2
child 1
child 2
<true>
bsh % schedule.step(state);
parent 0
child 0
child 0
parent 1
child 1
child 2
child 2
child 1
parent 2
<true>
bsh % schedule.step(state);
child 1
parent 1
child 0
parent 0
parent 2
child 2
child 2
child 1
child 0
<true>
bsh % schedule.step(state);
child 2
parent 0
child 1
child 0
parent 2
child 0
parent 1
child 2
child 1
<true>
bsh % schedule.step(state);
child 0
child 1
child 2
parent 0
child 2
parent 1
parent 2
child 1
child 0
<true>
bsh % schedule.step(state);
child 1
child 2
child 0
child 0
parent 2
child 1
child 2
parent 1
child 1
child 0
child 2
parent 0
<true>
bsh % schedule.step(state);
child 1
child 0
parent 2
child 2
child 1
child 2
child 0
child 2
child 1
parent 1
child 0
parent 0
<true>
bsh % schedule.step(state);
child 0
parent 0
child 0
child 1
parent 2
child 0
parent 1
child 2
child 1
child 1
child 2
child 2
<true>
bsh % schedule.step(state);
child 1
child 1
parent 0
parent 1
child 2
parent 2
child 1
child 2
child 0
child 0
child 2
child 0
<true>