What are the requirements for using the high-back booster mode on the Slimfit 3 LX?

The high-back booster mode is designed for children weighing 40 to 100 lbs (18.1 to 45 kg), with a height of 43 to 57 inches (110.1 to 145 cm), and who are at least 4 years old. Ensure your child meets all three criteria before using this mode.