An improved restraint system is provided. More particularly, the improved restraint system can include a harness and a booster seat. The harness can be attached to a seat belt of a vehicle. The harness can include a shoulder seat belt guide member for attaching a shoulder seat belt and also a lap seat belt guide member for attaching a lap seat belt. The improved restraint system can allow a child who is otherwise unsuitable for using a booster seat alone to use the booster seat in combination with the harness.