Okay, now FOR SURE we have official confirmation about babby making from the official site.
Marriage
"As two characters of different genders deepen their bond, that bond may eventually change to love, and they marry." Their child (remember though, Japanese uses singular as generic) then joins the group, and can fight alongside their parents.
Translation from TheEnd from Serenes.
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http://img149.imageshack.us/img149/2664/7b7aaa038007832d461b28c.jpg