2 ideas
In 5th Grade my DD made a cartoon calendar. I think the teacher was looking for colored pencil drawings-she was creative enough to create her own cartoon character and put it in a different setting for each month.
In 1st grade we did calendars as gifts and did a variety of teacher directed art projects for each month-we started before Thanksgiving and always had to push to get done. We did ice crystal art with epsom salt for Jan, valentine collage-Feb, something with shamrocks-March, Easter art-April, etc I don't remember all of the ideas now-it was about 8 years ago.
I like the poetry idea-but it might be a little late to get 12 good poems from each child. How many students do you have? If you have 24 you could assign them each a month and have 2 poems per month and then let each child decorate the border of the page for his/her family.