Daydreamer,
Before my surgery, I was contemplating planning a weeklong vacation at the beach with the family. I wasn't sure if I'd feel up to it, but I found it gave me a goal - I didn't want to miss out on a week at the beach, so I made sure to do my exercises and whatever else I could to feel better. It worked!
As far as your little boy - I had a 4 year old and a 9 month old at the time of my surgery. We told the 4 year old that I was going to the doctor to fix a boo-boo in my head and that her aunts would be at the house with her and her little sister to visit and play with them while I was away. I also gave her some "jobs" to do while I was gone - helping her aunts by showing them where we keep things, helping to feed the dog.. just little things. I think that made her feel like she was a big girl for helping me out so much when I wasn't there. I also tried to keep her schedule as normal as possible - getting her to preschool and gymnastics, keeping her usual routine at home as much as possible. She did fine. When she came to visit me at the hospital, she was a little concerned about the big bandage at first, but once she realized it was still me, she was okay. She'd help me take walks down the hall and lay in my hospital bed and watch tv with me.
I think it's normal for kids that age to be apprehensive about it, but my plan was to show her that I wasn't afraid and that I trusted the doctor and that I was going to be fine once my boo boo was better.
The 9 month old, obviously didn't know what was going on - as long as someone changed her diaper and fed her, she was fine with it!
I wouldn't go too into detail about your surgery with your kids. Just keep it at a 5 year old level. They usually prefer to not know the details anyway!
Good luck!!
Lori