All BabyBjörn Bouncers can be used by your baby from birth (8 lbs/3.5 kg) until they weigh 29 lbs/13 kg (approx. two years old). The baby side should be used and the safety harness always buttoned up until your baby tries sit unaided or reaches 20 lbs. Once your child is able to walk or sit unaided, flip the fabric, and use the chair side as a chair for your child.
Note that there might be an interim period where neither the baby side nor the toddler side works for your little one. Store the Bouncer in a safe place until baby is ready for the toddler chair.