D.W.
I would be cautious, but do your research.
I checked on FDA.gov, and they have submitted for registration, there are multiple documents listed via this link:
http://google2.fda.gov/search?q=USANA&x=0&y=0&...*
I couldn't find anything that showed you shouldn't use them, and they appear to be playing by the rules by working with the FDA. But, I'd want to check with your pediatrician first to make sure your kids should be receiving the amounts of vitamins listed on the label.
Our pediatrician still has both kids on 1/2 Flintstone vitamin/day.
http://www.fda.gov/Drugs/ResourcesForYou/Consumers/Buying...