I wouldn't give any kind of vitamin pill - try this: put a vitamin in a dish of vinegar and wait 20 minutes. What's left? That's what is going to pass out of your child's intestines without being absorbed - if the stomach acid doesn't dissolve it, you're wasting your money. The gummies are much worse - most of those sit in vinegar for 45 minutes or more.
Flintstones and every other vitamin you can find in a grocery or health food store, even if it's in chewable form, has a warning label on it: "keep out of reach of children"! So why would you give it to your kids?
I disagree that you should pick out "extra C" or things like that - most of us are not qualified to mix and match vitamins, but we play "kitchen chemist" nonetheless. Every nutrient, vitamin, mineral, etc. works in conjunction with many other nutrients - so isolating a specific vitamin or just a handful doesn't work. That's the biggest marketing ploy out there - "Vitamin Water" (with different varieties that feature different vitamins) or different combinations of vitamins for you to choose among. It just creates a million products and increase sales, with no clinical studies to show results.
I think the only way to go - and I've seen so many amazing health results with kids who have switched - is to a comprehensive powder supplement with ALL of the vitamins, minerals, trace elements, phytonutrients and also DHA for brain development. I use something that's clinically proven and developed by the lead scientific officer in the development of infant formulas. Most of the junk available in the vitamin aisle is not made in the US and does not have much scrutiny over it. I use vanilla or chocolate flavors and it really makes up all the missing nutrients, not only from picky eaters, but from our deficient food supplies. The AMA recommended over 10 years ago that EVERYONE needs to supplement with a comprehensive supplement, preferably in liquid form (and the powder that you mix in water or milk has greater potency than pre-mixed things that either break down or have emulsifiers in them). I look for a government patent, clinical studies, and a guarantee.
Happy to give you more info if you're interested.