The policies and procedures of Alanon spell that out. Anyone can come to Alanon who is mature enough to sit at a table and participate. So that excludes babies and children who are not yet mature enough to sit at a table and share (or pass if they choose).
But I have been at Alanon meetings where people have had to bring their babies. It's not a weekly thing. I remember one mom was from out of town. When the baby gets loud, it's time to leave the room until he/she calms down.
But I did quit going to a meeting (not Alanon) where one mom was allowed to bring her toddler who crawled under our chairs and incessantly bugged his mother. People did not like it but did not want to be honest about it. Then another mom thought, "hey, why should I pay a babysitter when I can just bring my child here for free?" and brought her toddler. When I walked in and saw the second child, I just turned around and walked out.