These look like common Comet Goldfish, which to me suggest that they are a "feeder fish" not necessarily meant to keep as a pet. Was the fishtank you got these guys from jam-packed with a bunch of goldfish?

Feeder fish are often overpopulated and pretty sickly. Goldfish in general can be.... iffy.... If you look at the Ranchu, Lionhead, and Golfball breeds of goldfishes you can see that they are extremely over-bred to be almost pug-like monstrosities of genetic problems us humans find "cute". I also bet that the store you purchased these from didn't tell you how FRICKING HUGE common goldfish can get, either eh? Maybe they did. I know I always told customers that they could grow to be 10 inches and if they got too large for the tank that I would exchange the larger fish for a few smaller ones.

If you guys do pursue further down the aquarium hobby I would recommend switching to an African Cichlid (sick-lid) family of fish in a few years. Once you and your son develop good aquarium care habits you will find that they are no more work to maintain than goldfish, actually probably less work to maintain. Goldfish are one of the messiest fish to clean up after. African Cichlids are EXTREMELY colorful and active schooling fish who seem to show a bit more personality than goldfishes. The one problem is they are quite territorial and you have to be very careful when mixing types.

Some are even fun-to-watch ambush predators like crocs!