While artificial sweeteners may be a lesser evil than sugar, they seem to all have their problems. Sucralose will kill off gut probiotics because each molecule throws off 3 chlorines. Aspartame degrades into formaldehyde. Saccharin has an unpleasant aftertaste. Often just the sweeteness will still trigger an insulin response which will still cause an insulin swing and unstable energy levels, which leads to more eating.
Unfortunately, erythritol is probably made from GMO corn, but most xylitol probably is as well. Nevertheless, I use them both, and find them far superior to other choices. If you get erythritol with monk fruit, you don’t have as much GMO exposure. I use stevia drops to make lemonade, and find it quite good. Stevia products made with rebaudioside generally will not have any aftertaste.
Unfortunately, once kids get on junk food, it can be a hard sell to switch, but that is why they make the stuff. Rather than trying to talk them out of it, and have to deal with the resistance, it may be beneficial to show them videos of people changing.
Dr Lustig may have some videos that could impact them. He specialized in pediatric endocrinology, and often talks about how he helped kids lose weight. Most kids drink plenty of soda. They don’t think sugar will make you fat. Fructose is one of the two sugar molecules in table sugar and is converted into retinyl palmitate. Palmitic acid is saturated fat. This is why kids are getting fat - not because of dietary fat.
https://youtu.be/LQZ9BPSS1_I Here’s a good one for the general problem that may have an impact on kids
https://youtu.be/dBnniua6-oM I’m not saying this is his best video for kids, but it may help you find one.
Here is a lady who talks about all the problems sugar gave her, and her quitting:
https://youtu.be/wVZ4PysHGyA
More general pointers: https://youtu.be/-s5szfPYKY4
A hard switch is probably going to be a bit rough, so maybe start with foods that kids can typically go for - a grass fed burger with trimmings on organic whole wheat. Chili made with grass fed beef and organic canned corn and beans. Look up “keto comfort foods.” Maybe find a grilled chicken recipe with virgin coconut oil or butter. Those are tastes kids can often go for.
What we did raising our kids was to implement a chip system, where they could actually earn chips by finishing their dinner, brushing their teeth earned one chip, doing chores, etc. When they earned so many chips, we would give them several choices for the weekend, and take them out - putt putt golf, a movie, an all you can eat buffet (yes, they had to eat vegetables to get dessert), etc. If they didn’t earn the chips, they had to stay home with a baby sitter… I don’t recall that ever happening… a word of getting left behind, and they were all over it.