There are two different questions here: do the antibodies transfer via breastmilk, and if so, does that provide immunity to the baby? This researcher (
https://www.mountsinai.org/profiles/rebecca-lr-powell) is doing COVID breastmilk studies. Here's one you may want to read:
https://plu.mx/mtsinai/a/0-XdDSQqqLez2w_MpnNX-YAIQ7PHldt7esNHWXI3g-s