For myself, I take B-complex, a lot of VitaminD besides daily sun exposure that tends to be shirts/shorts, calcium-magnesium-zinc, and fish oil. I try to get a lot of my vitamins and minerals through fruits and veggies thus meat will supply b12 and iron. I
I do the fish oil/Omega3's because of mainly the ability to aid recovery in minimizing inflammation, especially since I can't afford grassfed/organic meat and produce. That and I don't like especially liked cooked fish preferring ceviche and sashimi which are quite expensive not that shrimp is cheap either. Omega3's are very important for brain development in youths however besides the other heart health. While we can get Omega-3s from meats and eggs, it is a reduced amount compared to grassfed though I haven't been able to find exact numbers of Omega3's in non grassfed animals. It's gotta be some to some degree.
Perhaps if your child has an aversion to pill swallowing because of gag-reflex you can use a liquid form (which tends to be more costly). Too much in any dosage in some vitamins means you can't absorb it all at once and it becomes "expensive pee". Bigger dosages are cost effective but to a moot point if you are excreting it.