The size was chosen as 60 because the description mentions "around 3 months." It fit just barely on a relatively large baby of 6 kg at 3 months old (⁠ꈍ⁠ᴗ⁠ꈍ⁠). The neckline is wide, so it can be put on from the feet even before the baby can hold their head up. I used it for monthly photos.