While it is often difficult to find childcare, especially if a wedding requires travel, weddings are also formal events that are not necessarily made for children. Exchanging vows of commitment in a seated ceremony, sitting down to a dinner with a series of emotional speeches from family and friends and an open bar is not exactly a "kid-friendly" situation. While some couples make their weddings more inclusive for all ages with flower girls, ring bearers, kids on the dance floor and a dessert or ice cream "bar," the two people getting married should be the ones who decide their guest list. Of course, there are many children who can behave themselves perfectly at events, but a screaming toddler (who won't remember their aunt's wedding day) throwing a temper tantrum during the vows is usually not ideal.
If you choose to have a child-free wedding, you must accept that some parents will not be able to attend without bringing their children. Then again, demanding that there are no children at your wedding also means the only risk of the venue getting damaged or drinks spilling all over the white tablecloths will be from your cousin in college or your fun aunt hitting up the tequila shots at the open bar.