Klum, 33, and her singer-songwriter husband, 43, are in New York City working on "Project Runway," which will be broadcast July 12 on Bravo.
The couple have a son, Henry, 9 months. Leni, 2, is Klum's daughter from a previous relationship with Flavio Briatore, a race car driver.
"You'd never have known if you saw her at the Council of Fashion Designers of America Awards," a source said of Klum's slim figure earlier this month.
"She loves being a mom," said the source regarding their family life.