No, you will be reseated, most likely at check-in. I believe the minimum age for sitting in an exit row is 15. (My son's 14 and he's too young.) You're best off to call now and try to get your children in seats close to you - perhaps across or immediately behind.

FWIW, I have snuck my son up to the exit row before - he's 6' tall, looks much older than he is and reads every safety card inside and out. In short, I trust him to follow appropriate procedures and have the strength to handle the doors far more than most adults I see in exit rows. He was asked no fewer than three times on this particular flight how old he was.