I don't think anyone is going to "wrangle" with the idea of what to do with their kids for one hour every week at 11am on a Sunday. More than likely, they will just sleep in.
One person at the UU church in the area that I chose to not attend made the suggestion that UU was for atheists and agnostics who wanted their children to get religious education, so that nobody would do so is underestimating the admittedly small number of people today who go to church not for their own sake but that of their children.
Again, these are old people raised by the actually religious. Two generations removed from devout religion, people aren't going to care about "religious education". Also, if for some reason you do just want to educate your children that Christianity is a thing, there's the internet.