The biggest risk with a gun is cross contamination. It's impossible to fully sterilise them. Needles are sterile and single use. Yes, many people have no problems at Claires or wherever, but many people do. The amount of mopping up after them that professional piercers do is greater than you think.
At the end of the day, any body modification, even just getting your ears pierced should be taken seriously as it comes with risks, hence the stringent attitude of most professional piercer, and the fact that the tattoo and piercing industry have their own regulatory body - the APP - to keep up with best practise and changing regulations.
My DP used to do a first aid course every year too. Some people faint, vomit or have health conditions that need to be factored in.
People getting pierced at DPs clinic had to fill in about 20 questions before being pierced, and they reserve the right to refuse to do a piercing if it was likely to be problematic.
Recently things tightened up considerably after some modifications lead to a well known piercer and body mod specialist being prosecuted as there is a grey area around whether it strays into unlicensed cosmetic surgery territory.
It may just be lobes for your 8 year old, but it's livelihood and reputation for piercers, many of whom are doing it because of far deeper reasons than the cosmetic. And the last thing a professional piercer wants is for the person they are piercing to suffer unnecessarily, especially kids.
Of course every piercing comes with a risk, and some will go wrong regardless of how / where it's done - some people are just unlucky, and quite a few will disregard aftercare instructions and blame the piercer. Nothing is perfect but statistically needle piercings done correctly tend to have a better overall outcome.
Was with DP for 11 years, and heard plenty about it all.