As a teacher I agree with MadB's point on the difference between counting and reciting numbers. Also, the fact you say he is interested in counting is also a good sign. It shows he know it has a use, especially if its in conjunction with things you said like counting crackers and stuff. If it were me I'd just count things with him whenever the opportunity arises. I wouldn't make a big deal of it, even if its just you counting out the crackers and him listening. If its something he hears all the time he will pick up on it and not have to specifically learn or be taught it if you know what I mean? This has been the case with my DD and the kids I teach (I teach special ed).