Chen, Ran, Orin, Nazrin, Shou and many other kinds of beast youkai would have youkai cubs, as opposed to humanoid children. Wriggle and Yamame would even spawn hundreds of enormous larvae and spiders. They'd all eventually grow up into humanoid forms however.
I doubt the Scarlets would be able to bear children, considering they're 1) undead and 2) have permanently under-aged bodies. If they had kids however, it'd be safest for both mother and child if Flandre's offspring were to be raised by Remilia and the rest of SDM. Hopefully the result will be a refined lady, though she might take after Remi and become more brattish.