This is such a unique and cute item. It’s definitely breathable for your baby on a warm Spring or Summer’s day. It may work in autumn as well, especially if you live in a warm climate. The color is perfect y for a fall photo shoot! I am not sure of the sizing, it looks a bit large for a newborn. It may be 3-6 months. It measures:

Shoulder to cuff 13 inches.

Waist is 13 inches across but I think it’s meant to be big, like a dress.

Legs are about 6.25 inches across.

Shoulder to shoulder is 11 inches.

Please let me know if you have any further questions.