The 1 day old hatchlings have TTX. See Williams et al., 2011, Ontogeny of Tetrodotoxin Levels in Blue-Ringed Octopuses: Maternal Invesment and Apparent Independent Production of Offspring of Hapalochlaena lunulata. J. Chem. Ecol. 37:10-17.
Thanks @Neogonodactylus , I could read the abstract and a bit of the first page but, not being a student, don't have a subscription to Springer. I DID add this link and one recent PDF I found from your group to our Cephalopod Species (by family) Octopodidiae -> Hapalochlaena - Blue Ring Octopuses page. If there is a PDF or free access site, please let me know and I will change the link. Interesting that TTX was found in O. bocki's digestive system and the mention in an Abdopus. Guesses suggest that it may be quite common but only a few animals have evolved to use it.