An adjustable baby carrier grows with your child rather than being sized for one stage. The seat width and panel height adjust as your baby grows, so the ergonomic M-position (frog position) is maintained at every age, from newborn through toddler, without buying a separate carrier for each stage.
Most adjustable ergonomic baby carriers in this collection are suitable from birth (approximately 3 to 3.5 kg) to 20 kg or beyond. What varies between models is the adjustment mechanism: some use straps and buckles, others use snap buttons, and some adjust each side of the panel independently for a more precise fit (as on the Isara Preschooler). The right choice depends on how often you resize, how many different wearers use the carrier, and whether you need to cover newborn through toddler in one product or focus on a specific stage.