I have been vegan or vegetarian off and on for years now. I have always had a problem with fatigue and cravings until I discovered the book "Eat to Live" by Dr. Furhman. Basically I have cut out all grains and starchy vegetables except for 1 or 2 servings a day. I focus on getting my carbohydrates and protien from vegetables, fruits, nuts, seeds and legumes. I also cut out all added fat...I use little to no oil. I do make sure I have 1 tbsp of flax seed a day and an ounce or two of other seeds/nuts for fat. I also add nutritional yeast to my veggie burgers...so that takes care of the B-12 for me and my family. The kids also eat dry cereal with soy milk some days.
I am overweight as well, so the bonus has been weight loss
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As far as for kids...my kids do fine with this or have so far. I do make them vegan junk food sometimes like the chocolate silk pie tonight for dessert
and I do buy the vegan burgers and other "fun" stuff for them sometimes. But, on the whole they eat what I eat cause it is all they are served and they are doing just fine. They are skinnier than most of their peers(not saying much these days), but very well nourished and muscular, for that i feel blessed and happy! I do make sure they eat enough fat by making fun freezer cookies(made out of dried fruit, fresh fruit, soaked nuts and seeds and blended into a paste and frozen). This is their "dessert" most days and also snacks. I think for kids the most important thing to do is provide healthy food in the house and allow them to eat as they want from those healthy choices...they will eat the right amount that way.
I think I answered your question even though it is a bit scattered...LOL HTH