If you are using Corid, make sure you are using the extreme dosage. I think it is 1 1/2 tsp per gallon but check their Canadian website for correct poultry dosage. Use it for one week given to ALL of your chickens. Mix it with the food so that you make sure they get some of them medicine in their system. Only give the medicated water (no fresh water during the treatment). Vitamins, electrolytes, etc. should be avoided for several weeks as they may make the problem worse.
Change the litter in the brooder often (like several times a day to keep them from walking on it). Clean everything when you change the litter (water, food dishes, etc.). And avoid picking up your chicks while they are being treated as you could be part of the problem and you don't want to stress them. Make sure to change your clothes often.
And finally, increase the heat slightly but no so much that they are panting. You want their energy going into getting well, not staying warm.
My chicks had this same problem. But after increasing the Corid to the correct extreme dose and following quarantine like procedures, it went away.
I hope this helps your babies get better. One last tip: make sure that you are not confusing this with just normal loose stool, which can be just a way for them to cool off.