What about InLiven? 1/4 a tsp for children, and you can hide it in smoothies etc my kids have it in nudie juice tho. SOOOOOO much better for them than multis from the shop.... its made from food not lab made. If you look at the ingredients, you wont believe they will eat that But they do without knowing.

https://www.bellybelly.com.au/misc/mivitality-inliven