At 6, it is still considered normal to reverse them (whether it is in writing or sounding them out). There are TONS of tools about helping with this confusion--but most pertain to writing the word. My favorite though that works for reading is to simply pinch your thumb and pointer fingers together. Keep the other fingers straight. The left hand will look like a b and the right will look like a d. Just as in the written alphabet, the b is to the left of d. When reading, if you come to the word bob, you can quickly check your fingers to see which it looks like.
However, my dd (dyslexic) who still struggles with this (mostly with writing) had to come up with her "own" way to remember. Nothing I offered (the bed rule, b sees d, and many others) worked for her. Maybe it is that way with other kids too. The connection she made had to be her own. (BTW: she came up with "B is the big B and b is the baby, see mom-- it is one head shorter. So, she checks to see if it is facing the same way as the big B--if not, she knows it is a d. Also, the word baby associates the sound for her.)
But, sometimes if she makes that mistake when reading, I will simply auto correct. She might start to read "dasket" instead of "basket". I will quickly, say /b/ and she will start over.