I'm doing the same thing. I'm thinking that you will build your rack as if you are building it for adults. When the juvies come along, swap out the big tubs with 2 tubs that are half the size. This may be too big...i will post a reply with some pictures.

edit:

Here's from RhinoRaxx:
http://www.boaphileplastics.com/rhin...sterilite.html