I'm not sure which/whose reaction you're asking about, so here's my take:
It's perfectly okay to have a child-free wedding.
However, babes-in-arms often cannot be left for hours with people other than the parents. Sometimes they can, but certainly not always.
So if you choose to have a child-free wedding, you need to graciously accept the fact that it means some people with children will not be able to attend.
Pressuring the mother and saying that other people have to abide by the same rules doesn't help. If my husband was asked to usher at a wedding and we couldn't bring a young pre-mobile baby, we would have to decline. It's just how it is.