Tabitha,
Love your idea! Do you have anywhere to grow the seedlings or will the students take them home?
I use daylilies to teach my plant unit for 7th graders. I have some materials ( handouts, power points, etc) that you may be able to modify or pull some information from. Here is my lesson plans
http://www.amgen.com/pdfs/aast...
You may also want to check out the AHS (American Hemerocallis Society) if you are not familiar with it.
Tree mail me if you are interested, maybe we could have some of my 7th/8th graders send information to help teach your 3rd graders. I may also have seeds to share as I have been lucky that several wonderful people have shared seeds with my class over the years.
Lisa