It was probably Amakacin (not sure on the spelling either). Have two people when you do the injections. One to hold the snake and the other to give the injection. Hold the snake firmly, but don't squeeze. He won't like it, but he will get over it.
All baby ball pythons are a little scared and with a good reason! All these giants grabbing him and sticking him with needles probably isn't very fun! Ball pythons aren't really the aggressive type. They would much rather curl into a ball than bite. He will forgive you eventually
I would recommend leaving him alone (no handling) until the antibiotics are done. Once he is feeling better, then you can start some short handling sessions. Most ball pythons are very docile. They are usually a little more active and jumpy as babies and get lazier as they mature. I don't think you should have any issues with your 6 year old as long as you learn to read the snakes behavior.