Providing a babysitter?

My cousin and I are both engaged, however she’s getting married first. We live about 5 hours (and many states) apart, so we each have to travel for the others’ wedding.

Everyone in her area that I know is going to be at her wedding. I have children, one of which is too young to be invited (the others are old enough to go, and are very excited). My issue isn’t that the youngest can’t come but that there seems to be some issue with them providing a babysitter for the wedding, and I’m not sure how to approach it. I will have a sitter available during my wedding for any of my family members to leave their children with, so I feel like my expectations may be a bit skewed.

What is considered reasonable these days for out of town guests and uninvited children?

Edited to add additional context: at her brothers wedding, the parents provided a sitter (same parents paying for this wedding as well).