That is not heat burn, it is nute burn.... The potting soil is probably a bit hot for the young ones. Just give them PH'd straight water and maybe give them some mistings in between watering's. Make sure not to over water them. Once they get their feet under them they should be able to handle the nutes in the soil. The fan should help strengthen them up a bit.You are not feeding them yet, are you?
Good luck, you are in good hands here..
