Carve a jack-o-lateen ahead of time and bring it to class. Have them record the appearance of the pumpkin before. Add baking soda, vinegar, and food colouring of their choice. Have them record the appearance of what happens to the pumpkin. Two documents are attached: One with just space to record drawings of the pumpkin, and one sheet for more advanced students or older age group (I am in a grade 1/2 split so one is for the 1s and one is for the 2s) which includes a written portion.