There are normally a couple of staff at the top of the stairs to the US Immigration waiting area in Dublin who check your forms (the green one and the white one) before they let you join the queue to have your forms checked by the US immigration officials (the folks in the booth who stamp your passport, take your picture and fingerprint you).
The last few times I've flown, I got the forms at check-in, so if your folks check in early, they should be able to clear security, get a cup of tea and sit down to fill in the forms while still having time to buy some duty free before heading downstairs to Immigration.