I know what you mean. Rufus is constantly trying to find ways to ventur onto the big wide world. Now that he's finished his vaccinations I bought him a harness and take him into the garden and dispite the fact that he's on a lead, he loves it! I wasn't sure whether to get it or not because when I tried the same thing with Oscar and Layla when they were younger, they just froze and point blank wouldn't move when they had the harness on. I even opened the cupboard the other day where his harness is kept and he made a lunge for it and dragged it out to me as if asking me to take him out!
He spends his life sitting, looking out through either the window or the locked catflap and is trying oh-so-hard to figure out why the catflap doesn't work!
Your kittens are going to love it after they've recovered from their op. Just make sure you give them adequate time to heal as they can get infections from the outside world but the vet will advise you on length of time (can't remember how long I had to keep mine in!) and also it takes a couple of weeks for males to become sterile (as with all species) as they can still have active sperm in their tubes for a couple of weeks.
I remember both Oscar and Layla were no different after their ops- I was hoping for a quiet couple of days (or even an evening!) and no such luck! It tends to be with males nowadays (well for all the practises round here at least) that the males don't even have stitches so you shouldn't have to contend with buster-collars either which will be nice and I remember that when Layla had her spay done, they glued over the stitches with a dissolving glue so that she coulnd't chew them which was great.