I worked intimately with a woman in her home (where she ran a nonprofit literary society) and she had never told her children about her BP. Her daughter, in college, was suddenly struck with it and had to bear the brunt of having to come to grips with the disease for herself, in her own body at the same time she learned it was hereditary and had come from her mother (and her father's brother, her uncle; she had a double dose in her family, from both directions is probably why she got it).

You say your children are young; I would wait until they are in high school, at least, after you've had a bit more experience with working with it, but would tell them a bit about the disease, maybe while taking your meds in their sight and explaining to them, if only to make them "aware" there's a chance they or their children could have inherited it. In my family we did not talk about my parents health issues and now that I'm older/an adult it is hard having a sense of what "could" go wrong/could be inherited because my info is only sketchy.