Infants younger than 6 months old infected by SARS-CoV-2 show the highest respiratory viral loads
https://academic.oup.com/jid/advance-article/doi/10.1093/infdis/jiab577/6438522
""
We analyzed the viral loads of 45,318 SARS-CoV-2-positive nasopharyngeal swab samples obtained in Buenos Aires, Argentina. Infants younger than 6 months old presented higher viral loads than any other age group.
""
Unless mother has been vaccinated, in which case babies get protection from mother and also milk.
Secretory IgA and T cells targeting SARS-CoV-2 spike protein are transferred to the breastmilk upon mRNA vaccination: Cell Reports Medicine
Babies are very vulnerable before immune system has developed further.
If one needed more reasons apart from proven danger to mother when their system is under very high stress to get vaccinated.
Another good reasons to have everyone attending the mother and baby vaccinated, such as midwives, nurses, family.
I suppose another consideration is that they are shedding lots, pass onto granny and all the relatives too.