I have 2 kids, they are 5 and 6 now, but when I first went on dialysis they were 2 and 3... and so I found it easy to prepare them for every surgery I had by just sitting them down and explaining it to them in the simplest terms possible for their age, that they knew when mommy was not home, she was gone, getting better.. and when I returned home, they had to be very careful with mommy b/.c mommy had some owies that needed to get better and mommy couldn't pick them up until her owies healed and stuff like that. My mom brought them up to see me during every surgery and even before and after my transplant to visit. They were prepared for the visit the same way, that they needed to be careful with mommy as she was healing, and they needed to leave after a short visit b/c mommy needed rest in order to come hom quicker and heal quicker.
I hope that helps some. Good luck!