@Sweetie420, yhea they might be just a bit underdeveloped, I still dont see the system you running, where the solution coming from where and how much it drips and where goes runoff, first thing comes in my head is, if that red thing its the dripper I see it really far away from seedlings, in clay pebbles the water dispersion its very poor on the laterals this could explain the lack of water and nutes on their root zone, having the notion that seedlings in rockwool or jiffys may stunt by overwater I can see that happen on the two smaller ones
π