Read stories focused on the number 100, or on 100th day celebrations, such as "One Hundred Hungry Ants" by Elinor J. Pinczes, "Emily's First 100 Days of School" by Rosemary Wells, or "I Can Count 100 Bunnies" by Cyndy Szekeres. Recount some of the things you've learned so far during the year, making a chart of the children's ideas. Re-read favorite stories from earlier units or display photos and art work.
Incorporate counting activities throughout the day. Provide several different small foods to make a "100 snack mix." Try mixing fish crackers, cereal, teddy bear crackers, fruit snacks, dried cranberries, popcorn or small marshmallows together. Encourage the children to count the items in their snack, knowing that most won't reach 100. Don't include popcorn in the snack if your students are younger than 3 years old, to avoid choking.
Ask each child to bring in 100 small items appropriate for collage work, such as stickers, sponges, noodles, beans, ribbons or shells. Place the items in small containers. Give each child a sheet of sturdy tag board and glue to make a collage using the various materials. One way to teach children to use glue correctly is to ask them to make "ladybug drops." Children can easily visualize how large a ladybug is and learn quickly to make small drops as opposed to large puddles. String 100 large beads, fruity cereal pieces or noodles onto yarn to make a necklace. These activities may pose a choking hazard or may not be appropriate for children under age three who have limited fine motor skills.
For an easy movement activity, try hopping or jumping 100 times. Ask the children silly questions related to 100, such as "What would you do with 100 elephants," or "What would you do with 100 popsicles?" Chart their responses or make a class book.