I'm not really invested enough in the question to debate it, but I know plenty of atheists (both with and without children) who are active members of UU churches because they get more of the things they value from a social community there than they do anywhere else, and this seems entirely sensible to me. What effects on your future children are you concerned about?
I am concerned that they will treat supernatural claims as reasonable. I consider myself rational enough to be able to put up with some of the crazy stuff many UU individuals believe (beliefs not shared by the community). I am worried that my children might believe them, and even more worried that might not look at beliefs critically enough.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.