I chose pillows as the object of this activity because it is light, soft and quite big for her, which she might find it to be a little more challenging but not intimidating.
I started by taking five of the many pillows we have at the living room and placed them in front of her. As I do that, I counted one, two, three, four, five. Then I just let her do whatever she wanted to with them for a while, then I would make a pattern with them, counting one, two, three, four, five as I arranged them nicely. So, every time when I arrange them, I would do the counting.
She would also learn to take instructions when I told her to "stack it" or "give it to Mommy" or "put it here beside this pillow".
Here are some picture of what we did.
First she stacked the five pillows I gave her.