The pattern is clearly and simply explained in 3 sizes which are

preemie - 41cm/16” chest
0-3 months - 46cm/18 chest and
3-6 months - 51cm/20” chest

Cardigan knitted as one piece up to armholes,

Let your little one get comfortable with this simple v-neck cardigan.
Indulge them with a lovingly handmade cardigan.
Cardigans are a must for all babies, over little dresses and baby gros, boys as well as girls, saves putting jumpers over heads