Phyllis Briggs wrote several animal stories for children, as well as three pony stories. By far the best known of these is her sequel to Black Beauty. As astute readers of Anna Sewell’s Black Beauty will know, Black Beauty was a gelding, and hence was never going to have had a son. My copy of Son of Black Beauty does acknowledge this fundamental objection to the whole premise of the book thus: 'in this book the art of the storyteller has been enlisted to produce what Black Beauty the horse could not - a son.'
The Pickles books are both early readers.
Finding the books
The Pickles books are tricky: Son of Black Beauty is very easy to find indeed in all its incarnations.