Of course if you don't have a small children in your life, you can get older children to take photos, use your own art or use month-themed photos.
These calendars are so easy, you just need to scan or take of photo of their drawings and upload them to your favourite photo printer, granted that they make calendars ;)
12 is a great number for dividing things up. No matter if you have 1, 2, 3 or 4 children, it all works out to an even number of drawings for each child. But, when I 'only' had 5 children I found a way around it. For 2 of the months, they would each draw the same thing together on the same page, for example one Easter egg or one Christmas gift each.
When they were too little to draw but old enough to colour, I would sketch out a little drawing for them to colour in. This also served as a model for the older ones to copy. Hector was only just two when he coloured in these lily of the valley leaves.
It's also a good idea regardless, to sketch out sample pictures, making sure that you keep the designs simple. Not only is it easier for their little hands to draw, but they also tire of drawing so many. The easier it is, the better.
When they were too little to even hold a pencil I used photos of them with the theme of the month in mind.
On the front I always add our Christmas card photo for that year.
What is your go to Christmas gift?