McKenzie, who played the lead character Ryan Atwood and Reeser, who played series regular Taylor Townsend, snapped a photo together at the Zimmer Children's Museum 'We All Play' Annual FUNraiser in Los Angeles.
Since the show ended back in 2007, the former co-stars have both become parents with Reeser giving birth to sons Finneus, 5, and Dashiell, 3, while McKenzie welcomed his first child, daughter Frances, with fiancé Morena Baccarin last March.
Reeser spoke out about her character's relationship with Ryan (McKenzie) and the prospect of a reunion in an interview with People's Choice in 2015.
"It was a slow progression between the characters," she said.
"And I adore Ben, I loved working with him. We had a good working relationship, so it was a pleasure to get more screen time with him because I like him as a person."
She added: "I will always love Taylor and I would be so curious to see where she's at in her 30s. I would love to [do a reunion]. I would be totally down for that."
McKenzie currently plays the lead role of James Gordon on the Fox series Gotham and Reeser stars in the E! drama The Arrangement.