Charlie Westen is the son of Nate Westen and Ruth Westen. After Nate was killed and Ruth went into Rehab, Madeline Westen attempted to receive full custody over Charlie.
Following the events of "Reckoning", Madeline gave Charlie to Jesse Porter and told them to hide in the bathroom which they did while Madeline set off a bomb that not only killed herself but the agents sent to kill her.
In the aftermath, Jesse later gave Charlie to Nate's brother, burned spy Michael Westen and Michael's girlfriend, Fiona Glenanne, who decided to raise Charlie.