Gummy vitamins don't have iron, so unless he gets a liquid supplement in addition (really gross tasting and stain teeth), he's missing out on a very important nutrient. I still give my kids the liquid though, every so often in addition to an iron vitamin. I have to hold down the toddler to do so!
Some gummy vitamins don't have sugar. But that artificial sugar is probably worse (cancer, etc.), so we buy the kind with sugar. Also, only a few brands don't have artificial dyes.
Flintstone Complete has iron and it's a regular vitamin. They do have dyes but I cannot risk my kids getting low iron. We battled it getting a bit low and it causes irreversible IQ damage, etc. (iron deficiency does). It's a steep slope...as it gets worse. But anything low is NOT good. They took Dr. prescribed doses to get their iron back up.
I take gummies. My husband does. We love them! We don't get cavities and never have. I don't mind the kids eating a gummy vitamin here and there but I have to be strict with iron, then.
We don't, though, buy fruit snack gummies. Those are probably really, really bad for teeth.
Bottom line is my kids have to get Flintsone Complete daily for the iron WITH vitamin C in (regular) orange juice to absorb the iron. They also take calcium/vitamin D gummies but in the evening so the iron and calcium don't block absorption. The calcium chews are chalky so sometimes I just buy the vitamin D gummies alone. They drink a lot of milk.