Yeah, I'm not sure about the fuses on the horn (definitely on the lights!) but just get some toggle switches off of Amazon (make sure they can support the amperage the lights put out!). BTW if you don't know, when lights are 12v and 100w (example) the amperage can be determined by w/v. 100/12 = 8.3Amps draw. Just a good thing to know...
So yea. Look for something like
this for some light switches (I've used a buncha these toggles, they work GREAT!) and maybe something like
this as a horn button (I wouldn't recommend that switch, but look for a momentary switch button!). And of course, batteries are easy to come by, but DON'T use a car battery. They are meant to provide quick amps and get recharged by an alternator immediately after, NOT meant to provide power for lights for 1 hr and not get recharged later....(IDK if the Torpedo has a little alternator, I am almost positive the mudhead does [isn't it electric start?]) Also, make sure you don't get ripped off on a battery. You shouldn't ever pay more than $40 for a 12ah 12v battery. And you shouldn't pay more than $25 for a 7ah battery...
This is the battery I have used on my Spiderbox for a while. 12v and 12ah. 12ah is a tiny bit overkill, but I plan on running a few accessories on the kart, so I think it is justifiable. And if the karts don't have alternators, you can do something like
this charger to charge a 12v battery. I thought I was gonna have to use it to charge my batt and bought one, but it turns out my Spiderbox's alternator charges it, but when I used it it worked well. And of course you can use a solar panel to charge it, too (
here)
Good luck! I hope your kids have a blast!