Pumpkins are beautiful and varied, and so are apples, plus they taste good. No wonder these fall crops are part of early childhood activities in so many programs. Accomplished early childhood teachers don’t just “do” pumpkins—they use pumpkins as a platform for deep learning about a concept, such as life cycle changes in living organisms.
Marie Faust Evitt describes how her students use pumpkins to learn about measurement on the Gryphon House, Inc blog.
“Gourd-ous Decomposition” by Amy Rubenstein, Stacey Cleary, and Christina Siry, in the September 2009 Science and Children, describes an in-depth observation of a pumpkin before and while it decomposes.
Karen Ansberry and Emily Morgan, authors of More Picture-Perfect Science Lessons: Using Children’s Books to Guide Inquiry, Grades K–4 write a “Teaching Through Tradebooks: Pumpkins!” column in the October 2008 Science and Children about making observations, asking questions, and designing a simple investigation. (Note that some of the NSTA journal articles are free to all and some require membership. Join the NSTA Learning Center  at no cost and search for resources, free or otherwise, and join in the discussions in the forums.)
Here is a song to use while becoming familiar with the feel and heft of pumpkins. Pass around a variety of sizes of pumpkins while singing (to the tune of Way Down Yonder in the Pawpaw Patch)
Pickin up pumpkins, pass em to your neighbor,
Pickin up pumpkins, pass em to your neighbor,
Pickin up pumpkins, pass em to your neighbor,
Way down yonder in the pumpkin patch!
After planting pumpkin seeds, and harvesting pumpkins, your students can learn this chant (with apologies to Laura Joffe Numeroff who inspired this with her book, If You Give a Mouse a Cookie):

If you give it some water, it will grow to the sunshine.
If you give it some sunshine, it will grow some roots.
If it grows some roots, it will grow a sprout.
If it grows a sprout, it will grow a vine.
If it grows a vine, it will grow a flower.
If it grows a flower, it will grow a green pumpkin.
If it grows a green pumpkin, it will grow into an orange pumpkin.
If it grows into an orange pumpkin, you will pick it.
If you pick it, you will make a jack-o-lantern.
If you make a jack-o-lantern, you will save a seed to plant.
If you save a seed to plan, you will need to give it some dirt.
And if you give a pumpkin seed some dirt…
(Repeat)
If you are lucky enough to have a pumpkin plant growing nearby, you and your students can draw the leaves and flowers, and look for tiny pumpkins that have just begun to grow at the base of the flower. Investigate other flowers to look for similarities in flower structure and to see if a seed-bearing fruit grows where the flower was.
A class of two-year-olds ably dissected the leaves and flowers of a zucchini plant using scissors and plastic knives. We teachers were surprised to find that the stems are hollow! Using magnifiers made it easier to see some of the delicate structures. I rubbed off most of the prickles beforehand to make the experience more enjoyable.
Perhaps your students will begin a Pumpkin Project, similar to the “All About Potatoes” project conducted by 3-to-5-year-old children at Bing Nursery School under the guidance of their teachers, Jane Farish and Mark Mabry.  Read more about the Project Approach at http://ceep.crc.uiuc.edu/eecearchive/books/projcat2.html
Then write a comment and tell others about what your class does with pumpkins or other fall fruits.