Re: seat belts on the neck
If that is the case, it sounds like they may not be quite big enough to be out of boosters. Unfortunately, there are many vehicles where the seatbelts don't give a proper fit for anyone much smaller than an 50% percentile adult male. While the general guidelines to be out of a booster are 8 years or 4' 9" tall, the best guidelines are based on fit. Also see Question 9 of the FAQ linked under the top banner:
user.mc.net/~carseat/faq.html#Q9
One solution is to continue using a booster, especially for kids under 100 pounds. Backless models like the Evenflo RightFit and Safety Baby Uno/Polo do a very good job if your vehicle has adequate restraint behind the child's head. Jupiter Industries is working on a booster specifically designed for small adults. Until then, perhaps a generic auto seat cushion might help for parents who do not get a proper fit in their seat belts.
Many aftermarket products that pull the shoulder belt down also tend to pull up on the lap belt. That really only exchanges one problem for another, so they are generally not recommended.
When you do shop for your next vehicle, definitely check to see how the seatbelts fit your entire family. Some vehicles have adjustable heights on the shoulder belts, even in the rear seats.
I hope that helps! Perhaps someone else may have other suggestions for you as well.
Darren