I suppose it would depend on what you are thinking of doing. If you are planning on non-fiction that explains the basic facts of different conditions, I have only seen those published by small presses that are very targeted. I suspect that large publishers would be less open to this sort of book. Picture books that seem to tell a story but are really trying to teach children something, no matter how valuable the information, are also a hard sell. The most commercially viable (in my opinion, take it for what it's worth) would be fiction where a character happens to have a particular condition, but the focus of the plot is on something that all kids can relate to.
I have a student this year who has diabetes, and her mom gave me a picture book explaining the condition. It was well done, but clearly a small press production. So you'd need to do some research to figure out who publishes those kinds of informational books.
Good luck!