As per the subject line - it's (very) applicable to my question here (and, I'm sure, many others), but isn't available!
A tag can be made by any user with 300 rep or more in case of graduated sites like Bio. To make a new tag just type it in and hit 'Enter'. In your case, you do not have enough rep here on Bio (you do on the Database Administrators stack, for that matter). Newly made tags remain devoid of a description (tag info) so it's appreciated if a user feels that a new tag is justified to provide a tag description (an excerpt and where possible a full tag description).
Now on to your specific question - would I, personally, support a new 'nurture' tag? No, I do not. We have the development and reproduction tags and I think the reproduction tag suffices for your linked question. Honestly, I do not see much benefit in another additional tag here. For a new tag to be useful a reasonable amount of questions need to exist or expected to be asked in the future. Given the (low) amount of questions being asked involving the nurturing of offspring in specific, I would vote against creating this tag.