You can be around a newborn on your period as there's nothing harmful about it.
There is no medical reason why it is harmful to your newborn or a newborn to be around them or hold the newborn on your period.
The belief that you cannot hold a newborn when on your period is simply a myth that stems from outdated cultural stigma about menstruation.
Some cultures also associate menstruation with impurity which leads to customs that restrict certain activities including being around or touching newborns.
It is perfectly safe for a woman to hold and take care of babies while she is having her period.