Thanks for the replies. You've given me some ideas. 

I've just purchased a blender, and they love smoothies. Are raw eggs safe? 
I've seen a recipe that uses powdered egg whites. 

They are currently getting a lot of fruit because it is summer and there seems 
to always be something on the trees or good at the farmer's market. Where 
we live we can also go out and pick our own watermelons for $3 a piece. 

However, I know that I can't control everything that they eat. They have 
birthday parties at school with cupcakes, candy as treats and prizes for 
school, snacks at the after-school program, food from the babysitter 
(although that will stop now that school is starting), and the meals their 
father gives them when they are with him. I figure that if I give them the 
healthiest paleo meals I can, they are at least better off than they would 
otherwise be.

Marianne