Family children were non-negotiable if we wanted to have family there. For family, and all but our most local friends, it was a distance wedding and expecting siblings in-law to attend without their children would have been deeply impractical.
We talked to friends. If they could and were happy to have babysitters that was great, but no one was put in the position of having to decline and the conversations took place before the invitations were sent.
Capacity was our issue and it was hard enough finding a hotel for 100 and there were limited options to go bigger. We invited guests in batches, so family, friends then colleagues so we could see where the ground lay on capacity.
The Brownies did parade at the church 
Some church congregation also turned up which was lovely.
An IL did a reading and toddler DN came up and tagged along. It was very sweet and added poigniancy to the words "when I was a child, I acted like a child". Not in the plan, but a beautiful, spontaneous moment.
Child-free weddings are very much "know your audience"
If the wedding is very small and intimate that's one thing, but the upset creeps in when couples are unrealistic about the needs of their family and close friends.