What are the Devaputra / Devaputta? I have occasionally heard about the Devaputra (Sans.) or Devaputta (Pal.), particularly in regards to Mahayana, but haven't been able to find out very much about what exactly these are, as a category or class. 

Presumably they are not the same thing as the sons (and daughters) of Devas in Hinduism (and in also Greek mythology), wherein they usually refer to the physical progeny of divinities, who are often have supernatural powers and are involved in heroic exploits. 

What do Devaputra mean in Buddhist thought?
At least based on the Pali Canon and its commentary, devaputta are precisely what you state:  sons of devas with comparable divine powers.

For instance, the Pali Canon's Samyutta Nikaya's second chapter is entitled, "Devaputta Samyutta," and collects discourses involving the Buddha (or one of his disciples) engaging with a devaputta.  (You can find free, on-line translations of a few of these discourses at http://www.accesstoinsight.org/tipitaka/sn/index.html#sn2 .)  In his introduction to the Wisdom Publication edition of the Samyutta Nikaya, Bhikkhu Bodhi writes:  


  The devaputtas, or 'sons of the devas,' are young devas newly arisen in their respective heavenly planes; devaduhitās, 'daughters of the devas,' are also mentioned in the commentary but none appear in this saṃyutta. The commentary says these beings are reborn spontaneously in the laps of the devas.... [I]t is surprising to find that several of [the devaputta] — or at least their verses — have already appeared in the Devatāsaṃyutta [which is the preceding chapter in which the Buddha engages with adult devas].... This suggests that the dividing line between the two classes of deities is not a hard and fast one, just as the dividing line between an adult and an adolescent is not hard and fast...  (Source: Bodhi, Bhikkhu, 2005-06-10. The Connected Discourses of the Buddha: A New Translation of the Samyutta Nikaya, Kindle Locations 1285-1293. Perseus Books Group. Kindle Edition.) 


Just to note, the referenced commentaries were likely written centuries after the Samyutta Nikaya itself, and thus have significantly less authority.  In addition, I know you expressed particular interest in Mahayana tradition and the Pali Canon is most closely aligned with the Theravadan tradition; nonetheless, this canon provides a basis for understanding much of the Mahayana cosmology.

I hope this helps,
Larry