So the kids can see the miracle of birth.
Children can learn about birth from books and videos.
This does not justify causing a litter of perhaps 10 puppies to come into the world in need of loving homes. Take a trip to the local animal shelter and see the sad results of many litters born for just this misguided reason. There is absolutely NO medical, physical or emotional reason that a dog or bitch needs to reproduce itself except to continue the species. You want to recoup your investment. I doubt there are many breeds more expensive to breed than Great Danes.