Thanks for both your responses.
"...if I go to the actual mother's profile to add a child, I can add the child without any warning. Adding a child from a father only works if the father only has one wife."
Thanks. I'll be utilizing the mother's profile henceforth. This type of basic design logic oversight shouldn't be tolerated...and, as you've both noted, it apparently takes heaven and earth to ever get these fixed...if they're ever fixed at all.
"...but nothing I can't work around."
A necessity for "workarounds" to deal with fundamental flaws in design logic should be an embarrassment to this or any other online enterprise...but I guess our collective wheel hasn't been squeaky enough on this one.