Here's a fun learning activity involving counting, estimating, and one to one correspondence.
You'll need a container (we used a large mouthed water bottle) and a number of small objects (we used matchbox cars.
Have your child guess how many of the objects will fit into the container. Then fill the container. You can count the objects going in and count them coming out again.
We did this several times in a row. And then Isaac lined up the cars on the windowsill.
For extra fun, change the container or the object you're putting inside. Does the number that fits inside change?