Do you want to introduce your children to opera, particularly Richard Wagner, but worry about the often questionable content of the stories? Clyde Robert Bulla, children's writer of many subjects, came to the rescue half a century ago, and two of his books are available for free on Archive.org. We have had a copy of his Stories of Favorite Operas for years, and I think Lydia read some of the stories when, even with them family-friendlied up, she was a bit young for some of what is, still, not always meant for the nursery crowd. Still, with Bulla, you know you are on fairly trustworthy ground; you are not going to get anything beyond general fairy-tales-and-legends sorts of violence and misbehaviour.
So, keeping that in mind, here are the links:
Stories of Favorite Operas (contains several by Wagner)
The Ring and the Fire (Bulla's retelling of Wagner's Ring Cycle operas).