12/02/2011 at 03:45 PM EST
and fiancé Eric Johnson are pretty sure they know what to expect when they're expecting
– if only they could agree.
"I think it's a girl," Simpson, 31, told PEOPLE at the New York launch of a clothing line that she and sister Ashlee Simpson
created. "But I don't know yet."
"I think it's a boy," says Johnson, who was on hand at Dylan's Candy Bar in New York along with future mother-in-law Tina Simpson. "We're pretty much at a standstill there."
But the couple plans to find out the sex of their baby.
"I don't think we can wait," says the former NFL player, 32. "Jessica is too honest about everything, she needs to know. I don't think she can hold that secret to herself."
Even if she's wrong about the baby's gender, Simpson promises her child will be well dressed.
"If it's a boy," she quips, "I'll put him in tutus!"