When someone says “Kids won’t understand how two men can be married” what they mean, what they’re trying to say, is “I don’t understand how two men can be married.” When they say “Kids won’t understand why their dick looks different from daddy’s” they’re trying to explain “I don’t understand why you want to be different from tradition.” When they say “Kids won’t know who’s the daddy and who’s the mommy” they are telling you “I cannot comprehend a world without very rigid gender roles, and as far as I know neither can anyone else.” If anyone can think of a counterexample, let me know, but from where I’m standing, it looks like every use of the “confused kids” argument is just people pushing their own incomprehension off onto some largely-hypothetical kids.