It is extremely easy to see whether or not the hen is feeding the new chicks. They will have a full sack on the front of the neck/chest area and if they are being fed.  The sack (called the crop) will be filled with a milky substance. As the chicks get older you may start to notice seeds in the crop milk, this is normal. If the crop is filled with air then you need to seek the advice of a good breeder or avian vet on how to release the air.