one of our pullets wouldn't eat after sustaining severe injuries from a hawk. she was little more than a month old. DD very patiently feed her sugar water with a eye dropper or very small syringe (i think that she might have had something else too from the vet, plus antibiotics).
she would carefully, and gently work one drop in her beak at a time, so that the bird had to swallow. btw, it did take time, patience, and finesse that even amazed the vet (who had given up). i hope your situation becomes easier with your chicks.
good luck. i hope everything works out for the best Pedro.