Ideally take a multi vitamin and a multi mineral, if you can. The levels of minerals in a combined tablet tends to leave a bit to be desired. By a brand like Solgar, Biocare, Higher Nature, Viridian, Pharma nord, Soloray etc. You'll be hard pressed to overdose on nutrients. I've recommended people many times over the years, for example when dealing with immune or suppressed mood, to increase zinc intake to up to 50mg, for the short term. In an average (poor quality) supplement from the high street you might not even see 5 - 10 mg. Remember the RDA doesn't indicate levels for 'good' health.
Fatty acids (Omegas). You can go to town on these, every cell in the body needs them. Ideally take a liquid. Better to buy high quality and do it right. If you take capsules then you'll be looking at taking quite a few to equal the liquid. Start on something like one tablespoon a day. Kids need even more EFA's than adults, that's when they need it for GROWTH. Another connection here with this and the East Asian people of this world. Generally a shorter race, but as time marches on they are becoming taller. This has been since the introduction of a western diet, which even this at least, will have some good fats in there somewhere, lol. Previously if you look back at the traditional diet they ate a lot less fat. Something like 15% v the western world's 40%.
Worst case scenario, you buy a high street average brand and take a couple of capsules a day...much better than nothing at all.