I’m just curious about how you all imagine the appearance of infant/juvenile Covenant races? I have a big interest in developmental biology, so the thought has always really interested me.
Yanme’e: Due to their similarities with Earth’s insects, I think they’ll have a larval stage after emerging from their eggs laid by the queen, just like lots of insects that undergo complete metamorphosis. But it’s possible that they may just emerge as a Nymph from their eggs if they undergo incomplete metamorphosis.
Lekgolo: Since they resemble Earth’s annelids, it’s possible that individual or pairs of Lekgolo worms reproduce through parthenogenesis as an asexual form of reproduction and undergo sexual reproduction as well. The individual worms have an egg stage and possibly pupate into large worms through them. I’m not sure about their gestalt colonies such as: Dipholekgolo, Mgalekgolo, Rhulolekgolo, Sbaolekgolo, Khantolekgolo, and Thanolekgolo. As is commonly hinted, I think they must separate into separate colonies when they get too large, forming the bonded brothers you commonly see.
Unggoy: They’re born from eggs. It’s established that the Unggoy reproduce abundantly as r selectionist creatures. As r selectionists, it’s possible that they receive little parental care and mostly fend for themselves from a young age within the harsh conditions of Balaho. According to the Halo 3 Bestarium, they have very short childhoods as well. I personally imagine that baby Grunts emerge from eggs as smaller looking Grunts (as with most of Earth’s reptiles); possibly with infant human style proportions such as larger heads, big eyes and even squeakier voices. They actually sounds cuter than regular Grunts! 
Sangheili: They apparently emerge from eggs that exist in incubation tanks. Their children, or younglings, live in communal societies and they’re typically not allowed to know the identity of their fathers – but are raised by an uncle. In Halo: The Flood, I think it was stated that Sangheili children enjoy hunting from an early age and are also taught to fight at an early age. I’ve imagined them looking like traditional Elites except with similar body proportions to young humans, just like juvenile Grunts.
Kig-Yar: They apparently lay eggs. I’ve imagined them coming out from eggs looking featherless and undeveloped, just like altricial birds. Although the opposite may be true and they could look well developed after bird. Maybe it differs across the different Kig-Yar subspecies (Ruuhtian, a T’vaoan, and an Ibie’shan).
Jiralhanae: Since they’re the most strikingly mammalian of the Covenant, it’s possible that they’re viviparous and give birth to live-young, just like Earth’s placental mammals and marsupials. It’s stated in Halo: Contact Harvest that young Brutes have difficult controlling the release of pheromones.
San’Shyuum: They also look mammalian with their fur. It’s possible that they’re also bearers of live-young. And since both humans and Forerunners found them to be seductively beautiful, it’s possible that their young also looked really cute to these species. I’m not so sure if that remains true for the ancestors of the Reformists with their genetic erosion and decline.
Keep in mind that these are just theories and speculation based off of what I know about Halo lore and the biology of different animals on Earth, which the Covenant are undoubtedly based off of. They all alien species so that have evolved independently from any of Earth’s species so things could be entirely different. Although we know that the Precursor’s influenced the evolution of all species and there probably will be paths of Convergent evolution.
Feel free to speculate yourselves. You’re also welcome to discuss other species such as Forerunner and the Yonhet. If any of this is actually wrong, please tell me! I haven’t read Halo: Broken Circle yet, and I’d imagine this reveal much more about Covenant society and biology.
