High-back booster seats with a 5-point harness are recommended for use by children approximately:

High-back booster seats with a 5-point harness are designed to provide the necessary safety and support for children who have outgrown their rear-facing seats but are not yet ready to transition to a regular seatbelt. The recommendation for use by children approximately in the weight range of 5-40 pounds aligns with the safety standards established for child restraint systems.

This weight range ensures that the child is adequately supported and secured by the harness system, which is crucial for their safety in case of a collision. The use of high-back booster seats is particularly important because they help position the vehicle's seatbelt correctly across the child's chest and pelvis, which is vital for reducing the risk of injury.

Other weight ranges would not provide the optimum protection that these seats are designed for; therefore, maintaining adherence to the recommended weight guidelines is crucial for ensuring children's safety while traveling in vehicles.