Season 1: 6 children
104: Charity
Street Children and Extras (unidentified)
107: TREASON
Noah Reid as Roger's son Kyle
108: Escape
Austin DiJulio as Jerico's son, other son/ unidentified
109: Gray
Robbi Jay Thuet as Casey Wellman
120: Brainwash
Young  Nikita- Alex Stapley and Connor Devitt as Bully

Season 2: 6 children
207: Half Life
Michael's Sister's Child (unidentified)
208: Darkness Visible
Kyle Downes as Peter and Kevi Katsuras as Sasha11 TIMES)
211: Psyshic Pilgrim
Marcus Spilotro as Louis Armel
215: Fuzzy Logic
Kris Lemche as Greg Hillenger
219: Last Night
Sarah Gadon as Julia, the gypsy girl

Season 3: 2 children
301: Looking for Michael
Evan Caravela as Adam Sammuelle
302: Someone Else's Shadow
Evan Caravela as Adam Sammuelle
303: Opening Night Jitters
Evan Caravela as Adam Sammuelle
304: Gates of Hell
Evan Caravela as Adam Sammuelle (memory sequence)
305: Imination of Death
Hannah Lochner as Young Nikita
311: Walk On By
Hayley Lochner as Young Nikita

Season 4: 2 children
410: He Came From Four
Michael Cera as Jerome
413: Kiss the Past Goodbye
Evan Caravela as Adam Samuelle

Season 5: 1 child
506: The Evil That Men Do
Evan Caravela as Adam Sammuelle
507: Let No Man Put Asunder
Evan Caravela as Adam Sammuelle
508: A Time for Every Purpose
Evan Caravela as Adam Samuelle
 

Intel credit:
 Cindy and Sandy