I'd like to draw your attention to Telling b from d, a page which explains the most effective method I have found to address the b and d reversal problem. Furthermore, the method works both ways, that is, whether the child is reading b and d, or writing them.
I'll leave it to readers to access the page directly for the information there. Here I just want to emphasize that the method, set forth by Ms. Romalda Spalding in her book, The Writing Road to Reading, is one that I found highly effective when working with struggling readers one-on-one.
One advantage this method has over other methods is that it is essentially tactile and can be effortlessly applied without impacting comprehension. Other methods, such as the common "bed" method, or the "ball and bat" method require a child to interrupt his concentration on the story line, then think about a bed, or a bat and ball, in the middle of the storyline. In addition to being an inefficient way to sort out b and d confusion, both methods also interfere with comprehension.
Hundreds of games, puzzles, and worksheets have been designed to enable a teacher or parent to "help" a child practice identifying b and d correctly. In my opinion, most of the time spent on such activities is wasted. I had many students come to me over the years, aged 9 or older, who were familiar with the "bed" method and who had undoubtedly had many opportunities to practice b/d discrimination via those games and worksheets over the years. Yet they still struggled with b/d confusion.
Then there was the child I worked with reported after vision therapy that he "never could tell which side of the circle the line was on" before vision therapy, indicating that all the beds, balls, bats, games, and worksheets in existence were never going to solve his reading problem. If you find that a certain child just never seem to get basic reading instruction, you are quite likely looking at a child in need of an examination by a developmental optometrist. If they don't get that help, you will find yourself continually trying to design games, worksheets, and puzzles to try to instill basic concepts because the curriculum you're using will fail to work with such a child.
Learning to read shouldn't be difficult. To the extent that it is, a physical deficit is probably getting in the way, and games and worksheets won't fix it. Children should be taught the code effectively, and then that acquired knowledge should be used for the purpose it was designed, to read worthwhile material, whether fiction or non-fiction. That said, young children do have difficulty sorting out b and d initially, and will benefit from being given an easy-to-remember, but tactile, way of deciding which one they are looking at or trying to write. The method described here does exactly that.
This isn't to say that a well-designed game or worksheet isn't useful. Many of them are, provided they are used to practice recently learned material or to check understanding of a concept that was just presented. Those materials should be part of a well-designed curriculum, not plucked from the internet in a usually futile attempt to find something that works.
That said, why pluck Telling b from d from the internet? Because it works, as you will find if you're a teacher and you decide to spend a few minutes explaining it in your classroom, or if you're a parent who has a child who is always confusing b and d. In either case, to get the most out of the method, be sure they are writing b (line first) and d (circle first) appropriately. After you explain this method, and follow up with some consistent reminders, you'll find that the beds, balls, and bats are no longer needed, and that's a good thing because they are almost certain to interfere with comprehension.