The dog neuter surgery, and spaying and neutering of dogs or cats in general does not "make a pet fat and lazy". In a healthy dog or cat, free of hypothyroidism or other medical disorders, overfeeding and insufficient exercise are the sole causes of a pet being overweight. Don't blame the dog or cat spay or neuter surgery if a pet becomes overweight.
Photo by Amber, Flickr CC license
The dog neuter surgical procedure is performed under general anesthesia and employs sterile instruments and a sterile surgical field. Medical emergencies can arise if a pet becomes infected during these procedures. No surgeon approaches a spay or neuter as if it were "routine" because each surgery is different from every other because each pet is different, and although neutering might be deemed a minor surgery, a spay certainly qualifies as a major procedure.
Castration of a male dog does not "break his spirit"... it is probably the most common routine surgery done in animal hospitals all across the country. IF neutering promoted undesirable physical or emotional impact on the dog, it surely would not e performed as often as it is. Plus every veterinary hospital would be required by law and ethics to have the dog owner sign a notice that they were informed of these possible bad side effects... but there are very few reasons not to neuter a male dog.
There are no medical, emotional or sociological reasons for a male dog to sire "just one litter". You are misinformed or misguided if you believe that "having just one litter" is somehow good for the dog psychologically or medically. And the emotional or educational benefit to your children to experience the birth and care-taking of a litter of pups should be a very carefully analyzed proposition.
Will your children accompany you to the animal shelter when you drop off those last six puppies you "just weren't able to find homes for"? If you do choose to allow your dog or cat to have a litter, please be certain that there are committed pet caretakers waiting and wanting to provide a home for them. Don't contribute to the pathetic destruction of tens of thousands of animals euthanized yearly in pounds and shelters. You do have the power and intelligence to make a difference.