I bet the MG is your problem. There's just too much food in there for baby plants, and every time you give them water, they're being fed. This is a problem because plants that age don't need to be fed.
I don't know if you'd be better off leaving them and hoping they recover, or getting them out of that shit soil and into something better. Hopefully someone who knows more than I do can give an opinion.
Next time you plant seedlings, I highly recommend trying a bag of Promix seed starting mix. It won't burn your babies like that MG is doing.
Good luck.