I am not fan of multis, not even for kids, but as a last resort it can be better than nothing. Just check the ingredients for nasties like sweeteners.
I found a liquid one that looks close to not bad, except that the vit C and vit D is in wrong form. This is for adults, so the dosage for a 6 year old would be half or one third.
Alive! Liquid Multi Citrus 30 oz
Alivesupplements are the ultimate Food Energizers - with more invigoratingnutrients from more natural sources than any other product
25 Vitamins & Minerals
24 Fruits & Vegetable Juices
14 Green Foods
18 Amino Acids
12 Digestive Enzymes
12 Organic Mushrooms
Have no idea if it tastes good, the taste may be covered if taken in orange juice or something.
The kids I have put on iodine; we have done this as simple as possible, starting with juice; a lot can be put into it.
Iodine goes easily in milk too, tea, soups, dinner etc.
Vit c as magnesium ascorbate powder is palatable for kids, in juice. Ascorbic acid too.
Natrium ascorbate powder in savory food is also an option.
A good diet + staying away from sweeteners, fluoride.
Using the best fats like butter and coconut oil. -is a good start if you`re not already there.
Selenium; Swansson has a great selenium capsule filled with rice flour and selenium methionine only. It is easy to open the capsules and sprinkle it over food, no taste. Some kids even like to chew this capsule.
Magnesium; glycinate, malate, citrate; goes easily in juices possibly yoghurt.
Vit B and C; powdered or liquid. Make sure he gets enough of these two.
Now food has a great vit B 12 liquid I use myself.
They also has a good tasting zinc lozenge; good to have in store if winter infections. It has 300 mg vit C and 25 mg Zinc + herbs in it.