> ...I find it difficult and almost impossible to deny my kids of sweet treats few times a week.
Children model their behavior off their parents and peers.
> Also I am addicted to fake sugar (Truvia/Stevia etc). I use them almost everyday.
Young children do not comprehensively understand the difference between actual caloric versus non-caloric sweeteners. If you are talking about young (> Are they bad than natural sugar or worst or same?
Behaviorally, I believe non-caloric sweeteners are worse for children. It is setting up a norm for them in their later lives that puts them at a disadvantage understanding nutrition, as they then ingrain into their habits a sweets throughout every day and every food norm that is increasingly difficult to dislodge when they grow into young adults and older.
Teaching my children nutritional balance is my goal. Balance to me personally is not the American or American-derived food pyramid, though. You will have to fumble your way through this, as pediatric nutrition research is as much all over the map as adult nutrition. Personally, I'm genetically deficient with an extremely strong family history of Type 2 diabetes, and I have very likely passed that onto my children, so my choices won't be your choices. In a developed-world context however, it is relatively safe to let them free-range (as much as they want) green leafy vegetables with minimal to no dressing. Free-range up to reasonable amounts of other vegetables that are predominately or contain lots of complex carbohydrates (like carrots, celery, etc., as long as the diet is filled with a diverse range). Sufficient proteins and fats depending upon what pediatric research you subscribe to that defines "sufficient" for pediatric developmental goals. Fill remaining caloric budget with complex carbohydrates with low glycemic values. As little processing as possible for everything. Tap water for hydration; not bottled, not ultra-filtered, not carbonated, not oil-flavored, not iced, not diluted juices.
6 years-old is when I was able to teach mine to simplistically read a nutrition label; at that age, they were able to see that a particular packaged food for example is overwhelmingly sugar, with little to no proteins, fats or complex carbohydrates, and willingly place it back on the shelf. It helps in my case that they are terrified of needles, then see me testing my blood sugar many times a day, and remember that I told them when I was younger, I ate too much sugar, and now have a disease that requires I eat as little sugar as possible. They don't want to have to poke themselves to draw blood now, so they are much more moderate in their sugar consumption compared to many peers.
If you didn't start them out as infants along this path, take very small steps over a long period of time, and model your own behavior for them. How small the adjustments, and how long a time period, is governed by the individual child, your creativity, and your parenting time/effort. Your tolerance to whining and fits over the world is going to end if they don't get what they want, as well. Offer two choices, both representing a moderately reasonable adjustment. Fasting for even up to a full 24 hours two times a year separated by 4-6 months each time is not developmentally harmful for children 5 years old or older if you encounter refusal to choose one of the alternatives; many children will do that just catching a really bad stomach bug.
As long as you don't react emotionally to tantrums, acknowledge their feelings that it is hard to change, etc., then change is difficult but doable.