The
Graco TurboBooster is great, but your son really still needs to be harnessed. 4 years old and 40 pounds is the bare minimum to safely move to a
booster seat, and kids under age 5 are more likely to sustain head injuries in a crash if they are in a
booster vs. a harness. Think of it this way: when a child is in a harnessed seat the responsibility of being properly restrained is on the parents, but when a child moves to a
booster seat the responsibility is shifted to the child. He can easily move out of position while the parent is concentrating on the road.
We're moving my
dd back to a harnessed seat because she is not mature enough to use her
Parkway properly, even after almost 2 years of "practice" trips (we use the
booster for short, around-town trips to get her used to it).