This sentence is curious as there is no time coordination...

this way?

Actually in English either version is fine (unlike, AFAIK, the Romance languages). The meaning is basically the same, so it can be left as it is.

absence of time coordination is bad in any language...it's just illogical.

@sacredceltic: Just curious, why do you think it's illogical? I think absence of time coordination could actually be used to convey subtle differences in meaning in some cases. (I don't think anyone really does that in English though. It certainly can be used in Lojban. "mi na PU djuno lo du'u ra CA bajra" means "It is not true that (before now) I knew that he (current with now) runs", and the logic is entirely sound.)

I'm really not trying to start an argument, I just want to know your reasoning, besides the usual prescriptive linguistic reasons.

I think it is quite straightforward: I couldn't know then something she now has, because that would mean I would have been able to predict the future...

Thanks. That makes sense. However, a lot of things begin in the past and then continue into the present.

In this example, saying "I didn't know that she has a child" could imply that she still has a child, continuing from before when she had a child (which is the part that wasn't known), so the child hasn't died. It's a bit of a stretch though. (I agree that it doesn't work at all in a lot cases, e.g. "I didn't know that he dies" is quite nonsensical.)

>However, a lot of things begin in the past and then continue into the present.

Yeah, but not giving birth to a child, though...

In the case of progressive actions, one should use a progressive form then, like "is/was having"

"Having a child" can mean either giving birth to one or simply being the parent of a child. I was using the latter (which can continue). So technically, the original sentence is kind of ambiguous.

Now that I think about it, native English speakers would probably interpret "I didn't know that she has a child" as "I didn't know that she is/was a parent" and "I didn't know that she had a child" as "I didn't know that she gave birth to a child."