Kath,

It's important to keep in mind how much total time you will have with the
kids and to keep in mind how realistically you can accomplish what you want.
Are these kids 1st graders, third graders, sixth graders?  Their levels of
understanding and ability vary greatly between age groups.  I taught a one
hour class on scientific illustration in which third graders drew green
peppers, whole view and cross-sectional views and added labels. It was a
great exercise, at their level of ability, and the children learned some new
concepts and drawing principles for how to depict volume and concavity, by
using highlights and shadow, etc. The subject was simple enough that they
could master it relatively well, and they loved the hands on experience.
Their little eyes glowed with delight as they carved the whole peppers with
plastic knives and observed and drew their specimens!

Lynne