What a great start! Having the children take "ownership" of their own plots, along with help, advice, and lots of encouragement from you seems like a good, motivating combination.
The botanical garden associated with my local university has a childrens' vegie garden area, and the produce goes to the Food Bank. The program has been very successful.
The National Gardening Association used to give gardening grants to schools working to set up gardening curricula in the classroom. You might check
www.garden.org to see if they have info. you could use or financial help.
You might also consider getting into raising worms. Their vermicompost contains plant growth hormones, and the beneficial bacteria and fungi help the plants and retard diseases. The kids might get a kick out of feeding them food scraps from home and scrap paper. For more info, check
www.wormdigest.org/ for related books and their Worm Forum to help answer questions.
It's great that you're doing this - all the best!