I agree with friend Bhariya. I had a flight from Delhi to USA a couple of years ago. It was safe and secure. You don't  have to worry about your parents. They will be fine. Just tell them to ask the airport staffs if they have any question and problem.

One more thing, it's better if they carry a couple of hundred Indian Currency incase if they would like to make phone call or buy something to eat in the airport. It's a plus point if they could speak hindi to the airport people.