If your child has hearing loss, he may end up seeing both the ENT and the audiologist. However, it is the audiologist who will actually perform hearing tests and diagnose the hearing loss. The ENT will help with determining if there is anything medically to be done about the hearing loss (for instance, if it stems from middle ear fluid or something like that) and to give clearance for amplification if necessary.
Where have you had testing done before? There are audiologists that are great with kids at Georgetown Hospital and other locations in town. One thing to keep in mind is that with young kids, it does often take multiple visits to get full information on hearing. There also are "objective" physiological tests like the ABR (auditory brainstem response test) that can be done to get an estimate of hearing if a child cannot or will not cooperate with behavioral testing. Ultimately, you want to keep trying until get the behavioral information, but in the meantime, the physiological tests can provide a starting point.