Hi, My six year old daughter had this surgery last year. They did her abductors, hamstrings and heel cords at the same time. She went for day surgery, but they ended up keeping her overnight, just to make sure she was tolerating her tube feeds and her bowels were okay before she went home. She was on morphine right after surgery, but did not need it past the first two doses. They switched her to regular tylenol by the evening and she went home the next morning. She had very little pain or discomfort (and she definitely lets us know when she is in pain!).
She was put in a modified spica cast (went from her ankles to her thighs and had a bar in between), and wore that for three weeks. Then they cut the top part off and she wore the cast from her ankle to just below her knee for another two weeks.
The one thing we did, recommended by our occupational therapist, was to buy some vitamin E oil and massage her "scars" once the bandages came off. It really helped to minimize the scarring and seemed to soothe her after a physical therapy session and in the evenings.
My dd has been loose and much more comfortable since her procedure. She used to "scissor" quite a bit, no matter how much we stretched her daily. Now her legs are relaxed and her favorite position is more of a "frog", which was impossible for her before the lengthening. It is much easier to change her diaper now also, which is an added benefit.
Good luck with your son's surgery!
Angela