Once your child can count (with one-to-one correspondence) at least to 3, you can start playing a "Sort and Count" game with him. Gather a few different items, varying in number from 1 to 5 (or 3 if your child only counts reliably to 3). Have your child sort the objects, then count how many are in each group and add the number tag to the group. You can also play with random numbers (for example, 3 of something, 7 of something else, and 2 of another thing). Here is a fun example with our breakfast.
Counted and labeled.
You can see how I set up the same activity, but with pompoms, on a tray for Bear when she was much younger. Here (scroll way down) it is set up with farm animals and Gaddy Nipper crayons.