Pulling from my time as a youth coach and once a year novice ref here but: be positive, yet realistic. Winning takes time so any given kid is gonna screw up regardless of their age. It’s perfectly normal. Keep their head up and tell them what they did right/well. Also tell them 1 (or 2 max) thing(s) they’ve gotta work on. It’s an even handed approach because it teaches them that progress can happen in bad matches and there’s always something to sharpen, big or small.
As for tournaments, novice tournaments are your friend. Especially if they’re 6U, 8U, or 10U. Kids 15 and under shouldn’t be cutting mass amounts of weight. Their body needs fuel and nutrients, not starvation and the development of poor relationships with food. A gradual descent over the course of a season is fine. But it has to happen with a good diet that is feeding their body. After all, weight loss ultimately comes down to calories in versus calories burned so it’s vital that they are taking in nutrient dense foods. Round robin tournaments and/or Madison weight classes are extremely beneficial as well. I currently coach JH and I try to sprinkle in at least 1 or 2 round robin tournaments a year so my less experienced kids can get as much quality mat time as possible.
When it comes to technique/practices, it should largely be focused on the basics. Learning how to use your body in a way that works together rather than against itself. I always tell my kids that everyone thinks college wrestling is this big top circus where you learn all of these cool, unique tricks. In reality, you’re refining your fundamentals and positioning a lot of the time. The best guys are so unbelievably fundamentally sound, you can’t get them out of position because they’ve been in that position 1000’s of times before. If they’re a novice kid, practice should be FUN. Tumble, do gymnastics, practice simple things like getting in a good stance or running a half. Those will help kids learn strong fundamental skills that will help them throughout their careers rather than just win immediately.