Pull the pages of each month out of the calendar.
Tape them in order side by side on the wall at a level the children can reach.
Compile a list of the children's birthdays; this is for your own reference only.
One at a time, have each child tell the class when his birthday is using ordinal numbers, then find and circle the date on the calendar.
After all the students have taken a turn, have a conversation about the exercise using ordinal numbers. Ask questions like, "Who has a birthday on the first day of the month? Does anyone have a birthday on the 15th?"