LOL You're talking to a veteran technician with 17,000 posts here. I'm a moderator, and this is what I do for my job. I've worked with KDMF to install seats to needy families. I've done my research. I commend you for being an advocate for child passenger safety. Your children are by no means unsafe, and you need to make no changes to them. Nor are we saying you should.
However, I'm going to turn it back on you. Find me reputable sources (KDMF has already been shown as NOT being a reputable source) that shows that a six year old 45 pound child is safer in a harness. Yes, the harness disperses the forces over more points. It keeps the body in the seat. The Swedes think this is a terrible thing, since that puts ALL the movement on the head and neck, and doesn't allow the neck to remain stationary in relation to the rest of the upper body, thereby possibly *increasing* neck injuries. They go from rear facing to booster.
Most boosters and cars don't mind if you lock the seatbelt on a boostered child.
A child over 40 pounds has little risk of submarining out of a booster seat. That's why they don't have anti-submarine straps. The one that does starts at 40 pounds. So we're a bit baffled by it.
What we do know is that a child of the right age and size (at least five to six years old, normally, and over 40 pounds, unless that child is much older and a lightweight) is perfectly safe in a booster, just as they are in a harness. It's irresponsible to tell parents that a harness is the only safe option for your child over five. If you can find me reputable sources that say it is, I will happily and gladly read them.
There is one study I know of that says that kids under five are more at risk of head injuries in a booster. There's one study that I know of that says kids under 40 pounds are more likely to submarine in a booster. Though if the lap belt is low on the hips and fits well, even a 30 pound child in a well fitting booster is safe (we're talking a 30 pound six year old, not a 30 pound three year old).
Hang around. You're passionate. We like that. Just do YOUR research. We know all about KDMF. We were here when that hit the news. We discussed it ad nauseum. Search our archives for it.
http://www.car-seat.org/search.php?searchid=3274745 Those are the ones with "Kyle David Miller" in the title alone.
Wendy