Marvel Animated Universe
Cassie was kidnapped by William Cross because Scott had stolen money from him. However, Cross didn't know Scott had spent all the money in the treatment of Cassie. This caused Scott to steal the Ant-Man suit to rob banks to pay his debt to Cross. She was later rescued by Hank and the Heroes for Hire.
Cassie is the daughter of Scott and Maggie Lang. After the arrest of her father, her mother married with a policeman named Jim Paxton. Cassie was visited by Scott on her birthday (though Scott could not be there). Scott gave a very ugly rabbit toy, but Cassie loved it. Excited, Cassie told her mother that her father had attended the party. Days later, Cassie learned that her step-father was chasing her father, Paxton said he only wants to help him; she then said she did not want him to find her father.
Later, Maggie comes in to her room and Cassie asks her if her father is a bad man. Maggie replies with he gets confused sometimes.
A day before the big mission, while she slept, Scott went to her room to kiss her forehead and tell her he loved her. One night after, a furious Darren Cross went to Maggie's house to kidnap her and thus make Scott came to him for a final duel. Eventually, Scott went to rescue her which led to a super mini-battle between Darren and Scott. When the battle seemed lost, Jim broke into the room to protect Cassie from Darren as he sought revenge against Scott and his family. As Darren was ready to give the final blow, Scott decided to turn sub-atomic to destroy the Yellowjacket suit and save Cassie and Jim. Scott's plan was a success as he saved the lives of Cassie and Jim. After the battle, Cassie called her father to appear (thanks to that Scott fought to return from the Quantum Realm and go back to being normal size).
A few days later, she with her parents and Jim had a pleasant dinner until Luis called Scott to tell something very important. At dinner, it is revealed that Cassie took a giant ant as a pet.
The Avengers: Earth's Mightiest Heroes