Weddings are expensive, and there are a lot of ways they can go "wrong."
So it makes sense for people to invite people according to who they think will be respectful of the ceremony and thought poured into the details.
In recent years, the existence of "child-free" weddings have become more common for this reason. Cutting kids from the guest list reduces a lot of risks when it comes to emotional outbursts or chaos.
That said, the idea of "child-free" weddings is certainly a divisive one, since it can place more of a financial burden on parents to find child care. Or, depending on the age of the child - it can exclude someone who would genuinely enjoy the wedding.
At the end of the day though, it's up to the wedding couple to pick how they want the day to go, and who they want on the guest list, drama be damned.