Here's my suggestion for the December Calendar:
Why little boys in red and green? Well red and green are colors well know for their use in December.
Why little boys? I chose them because you can practice counting by 2's.
How many eyes do the 5 boys have? "Let's count by two's."
How many ears do the 9 boys have? "Let's count by two's ."
If each boy hopes to receive 5 gifts on Christmas, how many gifts in all would they receive?
If each boy does 10 kind acts, how many acts of kindness would happen this month so far?
If each red boy has 2 sisters, and each green boy has 1 sister how many sisters would they have. (on December 15th)
When you have little boys, it's easy to come up with problem solving situations for the group to solve.