This is a terrific way to approach it. I just might add - if you have a farm nearby with goats and/or cows or maybe a mother pig... take your child there to observe. Or a horse with her colt. Basically, any farm animal mom + kid. My daughters actually got to milk the goats - I signed them up for a camp. It was run by our city and was subsidized - a great option, which was both delightful and inexpensive. We have camps run by non-city farms as well, but their pricing is cost-prohibitive. But by the city - just great. If you go to your city's website and look for "recreation", you might just find that yours does the same. This is not for November, obviously, but for spring and summer. Right now you can find pictures of animals feeding their young. This is also a great opportunity to explain that birds lay eggs while mammals give live births and feed their young. Again, visiting a farm that has hens and chicks (not in Nov, obviously!) would be a great idea.

The reason your boy even wondered about it stems from our urban living, away from nature and animals. A child growing up on a farm would know the differences between the sexes by age 6, because he would have observed 6 seasons of mating, nursing, etc. You are dealing with an artifact of urban lifestyles.

If you have a zoo nearby, you can inquire from the administration when it would be a good time to observe nursing mammals.