Unlike some of you guys seem to do, I don't teach anything but Kenpo in my clubs, so the juniors learn Kenpo from day one.
In my clubs, a Junior Black Belt is the equivalent of an adult Purple with a Blue tip.
In the adult class they line up with the Purple belts (blue tip), because thats where their level of knowledge/skill is.
They wear a Black belt, with a white tip to show it is a Junior Ranking, and above the white tip they have a purple tip with a blue tip above that. (Denoting Purple rising towards Blue.
When the are promoted to blue belt, they'll have two blue tips, then a Blue and a green, then two greens, etc etc.
It's important to remember that with kids, you can't take their 'hard earned' Black Belt status away from them, as that would de-motivate them.
I spent a lot of time developing my junior syllabus, in consultation with two other Instructors, both much higher ranked than me, and I have been using it successfully for about three years now.
Les