During Halloween, I printed some flashcards with numbers on them. The children would them put counters on the card that corresponds with the number on the card.
I put dots to make it easier and then for Thanksgiving time, I put turkey cards without dots to see if they got the idea.
As you can see on the photo, the purple mat the child is using is a piece of cabinet liner I got at the dollar store. I then cut it to fit what space I wanted. These mats are then used during center time to define the space they are allowed to use.
This has really helped them understand that the whole carpet is not their play area and clean up has been so great.