Child seats for 2 year old - options?

[Hook'em]

It seems that there are two distinct issues being debate. Issues that have different factors.

First, most child safety seats work perfectly fine with a lap belt. On these types of seats, the belt holds the seat not the child. Since the original question concerns 1 and 2 year olds, the seat they are required to be in should be able to be held in place with a lap belt. (Lap belts are actually easier to tighten than shoulder belts in these cases).

Second, I do not know of any booster seats that work with only a lap belt (Britax makes a "husky" car seat for larger kids, but it is not a booster). By design, boosters are designed to "boost" children up so that the shoulder belt fits in the right location. In boosters, kids are held in by the car's shoulder belt, unlike the harness on a car seat.

I have a 3 and 5 year old and they can use a car seat held in my truck with the lap belt. Other than not letting the kids ride in the truck, I haven't figured out what to do when the car seat is too small for the kids. I have pondered installing aftermarket shoulder belts, but I am still unclear as to the law regarding aftermarket safety equipment and the actual safety of installing aftermarket equipment. My girls love to ride in Daddy's truck, but they will not ride with only a lap belt holding them in.