really? but even a human can have children with an elf...
If high/blood elves can produce children from mating with humans - the descendants of artificially created Titan constructs cursed by the Old Gods to a fleshy existence (basically Lovecraftian Pinocchios) - I think it is highly likely that they would be able to produce children from mating with their Kaldorei cousins.
A more interesting question to me is, are half-elf children fertile themselves or are they like mules (animals produced by mating horses and donkeys) infertile from birth as a result of their origins? It'd be interesting if that were the case.