Bo Hess is the daughter of Graham Hess, and niece of Merrill Hess in Signs.
She was played by Abigail Breslin, and this was her first role.
We first know of Bo when she screams to Merrill and Graham. The reason she screams is because a crop circle is found in their cornfield. Petrified, Merrill holds her. When we run into Morgan they enter a giant crop circle, one of three in a formation. Later on, Whodini tries to attack Bo. Morgan kills the dog defending her. Later, on, that night, Bo wakes Graham up, saying a monster is in her room. She then goes to tell Graham about things Coleen, her mother who passed away, used to say. All this happens, when both her and Graham spot a tall figure standing on their barn rooftop, causing Graham and Merrill to chase the figure. The next morning, Bo leaves cups of water on top of her TV screen. She then bothers Merrill and Graham with news. Crop circles have been found around the earth and aliens are talked about. Later on the family decides to go to town on Caroline's advice. There, Bo complain about the tap in her drinking water. When she joins the rest of the family at the pizzeria, we see them looking at Ray Reddy, the man who killed Coleen. Back home, Bo, along with the family, hear Morgan's baby monitor pick up a signal. We hear two creatures talking. Back, we see her playing with Morgan and the dishes, when a frantic Graham returns home, running. They watch news of UFOs over Mexico City. Morgan wants to use her tape to record the coverage, but Bo refuses. The next morning, she along with Morgan read a book about extraterrestrials. We see a very graphic drawing of a flying saucer attacking a house similar to their house, frightening all of them. We next see her with the family when they watch footage of UFOs now over 274 cities. Bo later tells Graham that she wants spaghetti, but Merrill suggest sandwiches to eat fast, so they can have more time to prepare for a potential attack. At the dinner table, Graham upsets Bo when Graham doesn't want to pray. Bo cries. Graham yells at her. Graham, outraged that the family doesn't want to eat, takes everyone's food. Graham then breaks down and cries and takes everyone and hugs them. When Graham and Merrill finishing boarding up the doors, being they can't board the windows, Graham tells Bo the story of her birth, saying she was a rare baby who smiled. Going downstairs, Graham holds on to Bo. When they go to the basement, Bo expresses her frightened state, after Graham warns Morgan that he's scaring Bo. When they finally barricade the door, Bo says she's OK. As a result of an alien hand grabbing Morgan and attacking him, when they final repel the alien in the coal chute and board it up, Bo cries as Graham tries to relax Morgan. The next morning, after revealing that aliens left quickly, and upon finding no sounds on the baby monitor, except for static, and after finally going upstairs, Bo dances in celebration of the alien's victory. But things turn bad when one of the wounded aliens, the one whose fingers Graham off a day earlier, captures Morgan. Bo then screams when the alien finally poisons Morgan, which backfires on them. When the alien is finally defeated, Graham, Bo and Merrill pray that Morgan is OK. Bo and Morgan can be heard playing with dishes at the end.