Learning with the calendar is a great way to focus your children's attention at the start of a lesson or as part of your daily routine. Many of the topics covered in the early years are naturally related to times of the year, seasons and holidays, so it makes sense to put them in context. There are so many things that the calendar can help you get started on ... and, your kids will take it from there! Mine have often been found "playing school" with the calendar as the center of activity.
Daily, go over:
Days of the Week - follow left to right progression, just like reading!
Months of the Year - beginning sounds get a work-out here!
Seasons - work in proper dressing, weather!
Related Holidays - share knowledge about each others' holidays!
Counting Up - practice any time you can! At the end of each week, practice moving down to the next line, just like reading :)
For more math practice, work in "Counting Down" to just about anything - the weekend, a special activity, a holiday - and "Counting by twos, fives and tens" as they are able. (I use different colors to denote the breaks when we are headed this way!)
As you work with your calendar, you will find many more uses and ways to build on the experience - and your kids will, too!