It’s a whole different ball game.
As Dom said, the rubber is the slippery part in the wet, so you run opposite of the racing line usually, going high in the corners and trying to avoid the rubber a bit in braking zones.
The biggest thing for a young driver who hasn’t raced in the rain before should be to mainly stay out of trouble, keep it on the black stuff, and don’t spin. Half the kids in the class are going to bin it trying to go fast, so just staying out there without going off is going to be both a huge accomplishment for your first time, and will net you plenty of positions. Rain racing is all about confidence and feeling the limits of the kart and trusting the tires, so building confidence by not spinning always helps. I would also say to look forward and pay attention, because odds are there are going to be some spinning or stranded karts scattered on the track.
In terms of driving, it’s a bit different in Cadet compared to a full-size kart, but in general you’re looking to get the kart to rotate at will, and you don’t have the grip you do in dry obviously, so you often need to make much more drastic inputs to get the kart to react. Here’s me last year at a wet race:
You can see that I’m throwing my entire body into the turn to get the kart to lift and rotate. Using your body mass can really help get the kart’s attitude to change in the wet. In general, leaning to wherever you need the grip is a good strategy. Kids have less weight to throw around so it doesn’t always do much for them, but it’s a good habit to get into.
For setup, the general idea is to go full wide on the front and full narrow on the rear. This induces the most mechanical weight jacking into the kart. You also tend to want a lot of caster in the front, as well as additional toe-out. But the track widths are going to be the main thing. It’s also a good idea to get a phonebook or some kind of seat cushion to sit on to get your weight up and let you use your body a bit more. Same effect as moving the seat up but less hassle. I have a big wad of towels wrapped in plastic and duct tape I bring along.
When you’re done, the clean up is probably the most annoying part, but we just coat everything in WD40 and wipe it down to eliminate rust. Make sure you flush out bearings and chains and everything, because a lot dirt and grime tends to build up in the rain.
Most of all, have fun! Rain racing can be super fun, as long as it isn’t freezing cold.