Chicco Neptune 123 Car Seat Specification.. This Chicco Neptune Car seat is a fantastic design and saves on the purchase of an additional booster seat in the future. Features Suitable from 9kg (approx 9 months) the intergrated harness will secure your child in place until they reach 18kg (approx 4 years). From 18kg the headrest moves upwards with your growing child and the in car seat belt secures your child in place. From 22kg - 36kg you can choose whether to use the seat with or without the backrest. The Neptune is fitted with special side protection for your childs head and shoulders.