Very, very sick parakeets

My son came to me a little while ago and said that his parakeets were just sitting on the bottom of their cage not moving.  Sure enough, they were both at the bottom of the cage.  He was giving them some millet when he noticed they were sick and they didn't even move to get the millet, their favorite treat.  They won't eat or drink.  I'm fairly certain they are both going to die.  I would feel better if we could figure out what has caused this.

These are the first house birds we have ever had.  My 9yo bought them in July of last year with his own money and was so happy to have them.  They have had fresh food and water every day, he has been diligent about cleaning the cage.  They seemed fine yesterday and even earlier today they were perching and acting pretty much normal.  In hindsight, I recall that they weren't as noisy this morning as usual, but it was a cloudy day and they aren't as active as early in the day when it is gloomy.

The only thing that has been different lately is we bought some millet from a new feed store.  It wasn't packaged, just loose in a bin.  They have had that as their millet for the last couple weeks.  Could there have been something on the millet that has caused them to become sick?  What else should we be looking at?  There are no obvious physical signs such as changes in their poop or cere, just all of a sudden complete listlessness.  No breathing trouble or feather picking. 

Is there anything we can do?  Everything I have read online and from what they are acting like, it doesn't seem like there is any hope that they will live.

*Sorry for cross-posting this.  I didn't realize until after I posted in the other section that there probably isn't much traffic over there and here may be a better place to get a fast answer.