It is definitely more difficult in the beginning and I don’t think it is ever too late. Eventually when you PROVE to him/her that you accept them no matter what, they begin to trust you and the relationship builds from there.
The first step is to get it through your head that you are dealing with a sick child (a choleh nefesh) and I mean that literally not figuratively. This attitude will make it much easier to follow through on what is required to help your child “heal”. Once you have accepted this fact we can move on to the next steps. However, without accepting this fact the process will be very difficult if not impossible to follow through completely.