^^^Whatever kids experience growing up is normal for them. Every family is the way they are, and most do a pretty fair job.
Why would anyone sit their kids down and try to convince them that their normal everyday life is not really normal? Having two moms is the way their household runs, just like having one young single Chinese mom, or one middle-aged divorced Italian dad, or two short fat Latino gay dads, or a young mom in a wheelchair and older dad with two working legs is the way other households run.
My husband is white and I am black. We never sat our kid down and said, "Honey, most people marry the same race. We, however are weirdos. Other people will tease you about it." It could just be that we are the normal people who recognize that race is a made-up illusion, and everyone else is screwed up!
There is no perfect, ideal Platonic model family out there somewhere that people should measure themselves against. Those perfect Happy Days families only ever existed on 1950's-style tv shows. In real life, even the 1950's family was a lot more diverse than the tv shows ever portrayed.