a) Watch them for 5-10 minutes. Healthy chicks eat and drink frequently while they are awake. If some are eating and drinking, the others will usually learn from them.
b) Gently feel their crops. The crop is where the food goes when they first eat it, before it gets digested. It's on their front at the base of the neck, often a little bit to one side or the other. The crop gets empty and flat if they sleep all night, and gets round and full when they eat a lot. It's common for a tiny chick to have a crop as big and round as a marble, or as big as the end of your thumb, at some times during the day--some people worry that the chick grew a tumor, but it empties out again as they sleep, and then they eat some more.
You might want to put some glass marbles or clean stones in the water dish. The chicks peck at them because they're shiny, get water in their beak, and decide it's good to drink. They also keep chicks from falling asleep in the water and drowning, or squishing each other into the water. (Chicks often do fine with no marbles in the water, but at some point I decided marbles are worth the bother to me for the first 3 days or so.)