It depends on your childs needs. Its best to speak to a doctor who knows what they are talking about like a naturopath or homeopathic doctor so they can provide you with the proper tests. A Multivitamin from Kirkman is great. Probiotics from Klaire Labs are great and enzymes from Klaire are great as well. You can never go wrong to start off with those three.

We stopped using gummy vitamins due to tooth decay now use Kindervital liquid multi vitamin have seen a difference in my little guys concentration and increased appetite

Agree with the above. Ideal world, you would have your son tested for vitamin levels. Until you can, I would supplement with a good multi like the above, D3 (many of our kids are deficient in this.. perhaps 1-2000 IU qd), probiotic (like Bifido complex), and a fish oil supplement (many of our kids need Omega 3 essential fatty acids).

if your son is not in any particular diet, you can ask your pediatrician for the recommendation or just get any over the counter directed for kids. if you want to use them as a supplement to increase his abilities, it will depend on the ingredients they add to those, and for that would be preferable to request an appointment with a doctor that knows about biomedicine, most dan doctors do. But along with that, they will probably recommend a bunch of other stuff...
My son has a kidney condition so, i wouldn't give him any supplement without consulting it first. anyhow, if he is eating right he may not need any vitamins and that can be determined through a blood test.

Thanks a lot everyone.