After sorting the marshmallows, he graphed them using the chart here. We practiced reading the graph to find out how many marshmallows he had in each category (without actually counting), and quickly determine which category had the most and the least.
J did really well on this. He waited so patiently to eat his marshmallows (I did let him eat the broken ones and the cereal as we sorted).
Here's another chart that would work well for coloring, but there's not enough space for actually charting the marshmallows.
Age attempted: 35 months