kids done see or taste them

Do not trust this though, if the kids are neurodivergent. If the picky eating is because of sensory issues, they might still notice, so be very careful with the amounts and types of vegetables. If they notice you are trying to trick them into eating something, that might damage their trust very deeply, and that causes all sorts of issues in long term. And they might refuse to eat the type of sauce again (or even all sauces you make), even if it does not have the veggies added.

Unless you follow the advice of cooking the sauce for a couple of hours, after which all that will be left of the veggies will be basically fiber.

To be fair, when cooking a sauce (or stew, soup etc.), some of the nutrients will enter the sauce (vs. cooking water that will later be thrown away), but preserving nutrients / vitamins etc. while cooking still means reducing heat / cooking time.

Please don't cook vegetables to oblivion and assume this will fulfill your kids nutritional needs. Not talking about you in particular, just making sure here.

That depends what you're cooking, I guess. I end up making lasagna or manicotti, and that could include any number of vegetables etc. If it will be served on plain noodles, adding veggies to the sauce itself sounds like a good idea.