Disclaimer: J.K. Rowling owns these characters; I do not.
They ran. They charged through crowds of people, not caring about anything but the fact that their son was in danger, their son could be dead by now, and they needed to get to him.
Now that he was in such danger, Narcissa felt like they had taken all the moments they had had with their son for granted; she recalled them now, vivid, perfectly clear. She thought of Draco as a baby, just handed to her after the birth, she thought of Draco accidentally setting the peacock on fire when he was seven, before he learned to control his magic, she thought of Draco picking out his wand. She felt like she was imagining his whole life and it was slipping by, it seemed like. One glance at Lucius told her that Lucius was lost in memories of their son as well.
Narcissa unconsciously reached for Lucius's hand as they ran. She clung to him, she needed him. If the unthinkable was true and Potter had lied or something had happened to Draco since then, she would need all of her husband's support and he would need all of hers. If they found him alive – she prayed that it was so – they needed to share the joy, it would not be complete unless they were there together.
They scanned what seemed like every person in the Wizarding world before they found him. It had been years since Narcissa had attended Hogwarts, but it all rushed back to her as she ran, and she thought of places that he might be. She was filled with a desperate sensation to check everywhere, everywhere for him, anywhere that was possible.
Finally they found their son, locked in battle with a seasoned Death Eater and holding his own. Narcissa felt her heart swell with a combination of fear and pride.
Lucius would take no chances now, he Stunned the Death Eater. Draco turned his head to see the source of the spell, and when he saw his parents it looked like a weight had been lifted from him.
It didn't take long for Narcissa and Lucius to run to their son. They all seemed unable to speak, unable to articulate feelings of love and appreciation and all the complicated feelings of family. Finally Narcissa found her voice.
"You're safe," she said as she put a hand on Draco's back, gripping him tight so that he wouldn't fade away, making sure that this wasn't a trick of the imagination. She turned and saw Lucius smile, truly smile, something that had not happened for so long.
Draco smiled too, at his mother's words or the brightness on his father's face Narcissa was not sure. It didn't matter, anyway. There was a battle still raging but it didn't seem to impact any of them. What mattered that finally they had a chance to be a family again.