Ask each child to predict how many seeds he believes are contained in the pumpkin. Write each child's prediction on a sheet of paper or on the blackboard so that a winner can be identified once the seeds have been counted.
Cut the top off the pumpkin with a sharp knife, then use a spoon to scrape the pulp and seeds out of the pumpkin's cavity and into a large bowl. Cover your work surface with newspaper. Drop a spoonful of the pumpkin on the newspaper in front of each child, and instruct her to separate the seeds from the pulp.
Ask each child to count the number of pumpkin seeds in front of him. Write all of the numbers on a piece of paper or on the blackboard, and encourage the children to add them to find the total number of seeds in the pumpkin.
Give the students an added challenge of counting the pumpkin seeds in multiples. For example, ask the students to recount the seeds in 2s, 3s, 5s and 10s. For example, if there were 200 total seeds, the students can make 100 groups of two seeds and 40 groups of five seeds.
Post a piece of graph paper on the wall, and mark each student's total number of pumpkin seeds. Once you've identified each student's total with a dot on the chart, create a bar graph showing each student's tally of seeds.
Consult the list of each child's seed predictions, and give a small gift -- or just a simple recognition -- to the child who most closely estimated the number of pumpkin seeds.