
Why is it a bad topic of conversation for a discussion board?
If I were in OP's shoes I would not take the youngest child on the trip. Amongst many other reasons, if the child had a serious medical issue related to his chronic medical condition while you were away and needed a hospital stay or was unable to travel for some period of time I suspect
travel insurance would not cover the expenses due to it being a preexisting condition underlying the medical issue. Pile that worry onto other concerns I would have about my child and I would not be able to relax and enjoy the experience at all.