The short of it is that a good buckle is worth shopping for. No parent wants to hurt their kid and it's easy to hurt them with the wrong buckle. When you help a child buckle their helmet you are often above them, making the area under their chin difficult to see. Even if you get down on a knee it can be hard to judge where the buckle is in comparison to the skin. Not only that but it's a sensitive area and skin pinched in the buckle will hurt!
As a parent you'll go through a lot to make sure you don't catch your kiddo's skin in the buckle. That might mean lots of extra time being careful but it can also mean making the strap looser so it's less of an issue. A strap that's too loose means the helmet is less effective and all the extra time isn't fun for anyone. Instead, look for a buckle that makes life easier with some kind of no-catch system.