Hewitt, 35, announced she's expecting her second child with husband Brian Hallisay earlier this month, reported E!Online.
"Jennifer is almost four months pregnant and doing great. They are loving being a family and excited about expanding. Jennifer knows having two children under two is going to be a lot of work, but she loves the idea of having her kids be close in age.
"Being a mom is the most important thing to her and she's thrilled about being pregnant again," a source said.
Hewitt and Hallisay welcomed their 14-month-old daughter Autumn back in November 2013.