We are called to be open to life, at any age. So yes, I want someone who understands and follows that, even at my older-ish age. For those of you who are younger, be careful of someone who isn't open to God's plan and life.
If you are trying to evaluate someone from their preference in number of children, I think that's a question that you can ask during your communications with the person.
That being said, I think this is one of the easiest things to change in someone else. Also, guys, I have learned, tend to put up how many kids they think they can afford rather than a particular preference. And folks who are only children thing they are being pretty wild by putting up 2-3. Personality types play a big part too...as the planner may rationally say, "well, if she is 32 years old realistically she only has a certain number of child bearing years left so this many is the right number."
Me, I don't plan such things. ;-)
As long as we are both open to the will of God, my husband and I should get along just fine.