"We are thrilled," Mike and Kelly told People magazine.
Myers and Tisdale started dating in 2006 and got married in a private ceremony in New York City 4 years later. They are already parents to a 2-year-old son, Spike.
The actor, who was promoting documentary movie about talent manager Shep Gordon "Supermensch: The Legend of Shep Gordon", said in September that he always wanted to expand his family.
"Anyone who tells you fatherhood is the greatest thing that can happen to you, they are understating it. I am the happiest I have ever been in my life. I knew I wanted to be a father, I didn't know it was going to be this awesome or that my kid would come out so beautiful and lovely," he said.