You might also consider getting "regular" classics and using Cliff's Notes. They get a bad rap because so many college students read them instead of actually reading the book--not recommended! But as a companion for self-guided study, they can be pretty useful.
You might also try H.D. for poetry. She has some interesting feminist revisions of Greek classics that would be pretty accessible for younger readers, I think. Especially if read in tandem with the Greek classics, it could lead to some interesting discussions.
Other favorites of mine that might be appropriate for children: Gwendolyn Brooks, Christina Rossetti, any of the romantic poets (Keats, Shelley, etc.), Shakespeare's sonnets, some Ezra Pound...You might consider finding a poetry textbook or anthology and just seeing what strikes your child's fancy.
Best wishes!
