Posed newborn sessions require a silent, peaceful studio and a zen-like concentration for the photographer.Even for siblings who are excited during pregnancy, the arrival of baby is a HUGE and very stressful adjustment that takes time - for both the sibling and parents. Young siblings, especially toddlers, are very demanding and emotional in the early days and parents are universally overwhelmed. Posed newborn sessions are held a week after birth, when sibling's feelings are strongest - which makes for a very difficult session for everyone involved.
Instead, I include siblings in a sibling and family mini session on a separate day (baby should be 2-6 weeks old, the later the better). By that time, parents are in a routine and feel calmer, the toddler is used to baby, and baby is awake and interactive, which makes for beautiful photos of siblings interacting and a better experience for everyone involved.