First thing you need to do is deal with the childrens seperation anxiety
by getting them accustomed to the fact that there will be times when you have to leave them for awhile. I am assuming that they are quite young because of this and can say that this is a normal process for all young children. You have to be honest with them about your health problems but do not scare them with too much information and upset them by crying ect.. Be very calm and matter of fact. Most importantly , enlist the aid of the people closest to you especially those who will be the childrens guardians and caretakers in the future in an effort to give the children a strong sense of security and love that will help them when the time comes. I hope this helps some and pray that you will be here for as long as possible.