I would think that bringing children is a "policy" and not a by-law. By-laws are rules that need to be enforced and often have consequences. A policy leaves some room for circumstance that are unusual. Often a simple quiet word form the president or leader is enough to check out why a child is in attendance and to reiterate the policy of children not attending meetings.
My guild is informal enough that we do not have by-laws. But that said, we highly suggest that children not attend quilt meetings that have a teaching/instruction component each month. We do encourage young sewers to come to quilt work days and even retreats. I had to bring my out-of-state visiting grand children 8 and 9 years old to a guild meeting and it worked out fine that one time. They were in the back of the room and busy with quiet activities. Not a problem. But I got enough "looks" to know this should not be a regular practice.