Since Kua-toa are walking fish (kind of like murlocs from Warcraft), are their young like large fish with appendages, or do they look smaller versions of the adults? I am playing D&D 5e, but if that edition doesn't have definite answers I will be curious what previous editions say.
Kuo-toa start life as miniatures of the adults, but fully aquatic unlike their amphibious elders. The AD&D 2nd edition Monstrous Manual/Monstrous Compendium, the premier publication in D&D history for non-combat information on monsters, tackles kuo-toa young as the first thing in the Habitat/Society section of the Kuo-Toa entry:
Kuo-toa spawn as do fish, and hatchlings, or fingerlings as they call their young, are raised in pools until their amphibian qualities develop, about one year after hatching. The young, now a foot or so high, are then able to breathe air and they are raised in pens according to their sex and fitness.
Notably it doesn't make any mention of the fingerlings having a different basic body plan than the adults — they spawn and hatch like fish do, but doesn't say that they are at all more fish-like than their elders apart from breathing only water. So in absence of that, they are just tiny kuo-toa, humanoid body plan with little arms and legs and all — only not yet able to breathe outside of the water.