Mark-Paul Gosselaar Nanny Video

Elizabeth Messina

Mark-Paul Gosselaar has a secret – but he’s not sharing!

The Franklin & Bash actor and his wife Catriona McGinn have found out the sex of their first child together, but the couple have decided to keep it under wraps until the September delivery.

“We have two names in the running,” Gosselaar, 39, tells PEOPLE.

Fortunately, the future father-of-three – Gosselaar is also dad to Ava, 7, and Michael, 9, from his previous marriage – doesn’t need to divulge too many details in order to solicit suggestions from his costar Breckin Meyer.

“Breckin Gosselaar, that’s unisex. It can be a boy or girl,” he says, prompting Gosselaar to admit the name has “a ring to it.”

Despite happily discussing their children – Meyer is dad to two daughters – the bantering between the costars quickly turns to their childcare – or lack thereof.

“I don’t raise [my daughters],” Meyer jokes, later adding, “I have a staff!”

“I have people do that … I have nannies!” Gosselaar playfully adds. “Basically we’re slaving away so that we can have nannies.”

But when Meyer clarifies that his children do not have nannies, Gosselaar jumps on the bandwagon, sharing, “I don’t have any nannies either. I don’t!”

All joking aside, according to Meyer, fatherhood was the foundation of the pair’s friendship. “It’s pretty fantastic being a dad,” the actor, 39, says. “I think that’s one of the things we connected with when we first started the show. We both are kind of family guys, family men.”

The season premiere of Franklin & Bash premieres Wednesday at 9 p.m. on TNT.

– Anya Leon with reporting by Michele Stueven