I want to say it would be better to put such a thing under "ethics." Hard-wiring those things in the species seems off somehow.
On the other hand, most non "sentient" species seem to work that way as far as our real-world observations have gone...hmm.
Maybe if it was a non-required tag for species. If the tag is missing in a species, all members tend to young depending on convenience. Non-civ species can take the tag in caste definitions. Civ species can take the tag in ethics under the format [CHILD_CARE_CASTE:<caste_name>:<ethic_descriptor>] or under the caste, but not both.
I think that might model things better, because once a species is thinking in intangible concepts, dogma, and traditions, child care becomes a sticky subject. For instance, if a father was the primary caregiver in a society where fundamentalist religion dictated that women are supposed to be taking care of the children, he could be exiled or imprisoned or something else horrible. Seagulls, on the other hand, probably wouldn't care at all.
Also, if gay couples ever made it in, just a caste-based tag would be kinda broken and the code behind it would have to be rewritten anyway to deal with it. Better to nip it in the bud and add opportunities for interesting stories for when we get a legends update. For instance: a defiant husband and wife raise their children together in a culture where the women are supposed to do it alone, constantly heckled by the townsfolk. Their children go on to conquer half the world and unite the human races.