I would say the damage was caused by giving them "bloom" nutrients with too much phosphorous and potassium being applied to young plants that are still very much in their "grow" cycle. Young plants need nowhere near as much of these two major nutrients when "vegging" as compared to when they are flowering. Also, young plants can do with quarter to half strength nutrient solution, as a much safer option, to prevent burning. It is far easier to treat a slightly underfed plant than it is to rescue one that has been over fed and burnt.
Try giving just plain water for a couple or three waterings, as this will allow for some of the excess accumulation of P and K to be flushed out/diluted, before returning to feeding them with a weaker "grow" nutrient mixture (1/4 or 1/3 or 1/2 strength), and the new growth should return to normal. Hope this helps,.... Organoman.