From what i'v seen sunni/shia marriages don't work out too well, when the couple has a child. Since its usually the girl who makes the sacrifice of converting, when it comes to raising the child, many times the couple is not on the same mindset, and she is forced to tag along her husband. There is nothing wrong with that, but i think it keeps those women from expressing exactly how they wanted to raise the child.
**Its a completely different story if both partners are not too religious in their beliefs, and they decide to raise the child in a mix of sunni and shai traditions.*