It doesn't 4 days
It takes 25-57 hrs for 1/2 of the cannabis
to be out of your system & several more for it to leave completely.
During the same period milk is being made continuously.It can reduce your milk supply, sedate the child, increase risk of crib death and infections. This is something you give up to be a parent, & in my state is considered reason to terminate your rights & remove the child forever.