Depending on the type of surgery. For laparoscopy, where the procedure is less invasive using keyhole surgery, you should be able to get up and move about within a day. However, do try to avoid strenuous activities or exercise (no moving of furnitures or do 2 weeks of groceries or get back to gym for at least a week.
For laparotomy, where the incision may be a bit bigger, your stay in hospital will be longer, say 2 - 4 days, and your body will take longer to recover. You are likely to be advised to stay away from strenuous exercise and only return to your normal activities between 4 - 6 weeks. I would err on the side of caution and go for 6 weeks. You can still do some gentler exercise to ease yourself back to the routine.

I would suggest tepid sponging. Or, take your son into shower with you and together, have a warm shower, slowly reducing the temperature. But never cold water, this may lead to the child having convulsion. The tepid water will help freshen him up and bring down the temperature of his whole body. Dry him thoroughly and let him drink plenty of fluid. Water, squash, keep him hydrated. That itself should be enough to bring the fever down. If the fever is not budging, you can try kids Calpol which you can get from any drug store. Instructions on the side of the box. All the best.