Those!

 is a Fallout 3 quest. It is also an Xbox 360 and PC achievement.

A lost, small boy called Bryan Wilks asks you to help him find his father, who seems to be trapped in Grayditch, while he takes refuge in a diner.

Find Bryan Wilks's father
The boy and his dad were attacked by fire ants. The father can be later found dead in his house by the shack, killed by the ants. You can loot a Chinese Assault Rifle off his body and the shack's key, where you can find the Doctor's equipment.

The mission after this is in the Marigold Metro Station to the southeast, where the fire ant infestation have to be cleared. Here you need to find Doctor Lesko, who is in a maintenance room. You can choose to not follow his mission and destroy the queen, but if you follow his instructions, and kill only the fire ants (nested in the hatchery, go inside the room where the doctor is located), you will receive a prize - a choice of either Ant Might or Ant Sight perk. With a speech check you can kill the Ant Queen and still get the perks.

Behind the scenes
This quest was inspired by the 1954 film Them!.

Find a place for Bryan Wilks to stay.

His aunt Vera owns the hotel in Rivet City. You just need to ask her about Bryan Wilks and she'll agree to take him in. Go back to Grayditch. And walk into the Wilk's family house Bryan is on the second floor in the bedroom sitting in a chair. Tell him to move in with Vera and the quest will be complete.