"Christian" mom and "muslim" dad for me, and that situation never happened because I had a secular upbringing.
Thankfully, neither of my parents were, what you'ld call, "practicing theists". My dad is somewhat more religious then my mom, but he's the kind of muslim that once in a while does ramadam as an excuse to loose some weight and then celebrates the end with a wiskey and pork chops
It is my opinion that a marriage with children between 2 "practicing" theists who are serious about their religion and clinge to different religions, is pretty much doomed from the starts - especially if it concerns "exclusive" religions in the sense that they believe that either you are part of their elite club, or you burn in hell.
As an atheist, I must say that I couldn't bear being with someone who is religious and actual serious about it. Kids especially would be VERY difficult, because I would simply not allow my kid to be brainwashed into some cult.
The whiskey and pork chops merely enforce the idea that nobody is perfect. Nor should God consider humans to be perfect. That makes God's punishments seem strange (flood the whole world because God made free choice and flawed humans?). It seems that mankind's sins are really God's sins for making us this way.
As long as kids are good people, it doesn't really matter what religion they choose.
We all have to stop judging others, and pay more attention to the log in our own eyes, rather than the tiny splinters in the eyes of the judged.