Mothers are encouraged to bring their nursing babies to church according to Scripture. The prophet Joel specifically called for mothers to bring their nursing babies to the congregation. This passage is read on Ash Wednesday.
From the book of Joel, 2: 15-16.
Blow the trumpet in Zion;
sanctify a fast;
call a solemn assembly;
gather the people.
Sanctify the congregation;
assemble the elders;
gather the children,
even nursing infants.
Let the bridegroom leave his room,
and the bride her chamber.