"When you're in the beginning of parenthood, there are so many embarrassing moments," the "Pieces of Me" singer, who also shares 8-year-old son Bronx with ex-husband Pete Wentz, told Us at a Lucky Brand event in Los Angeles on Friday, May 12.
One time in particular, Simpson, 32, and Ross, 28, scrambled to change Jagger's diaper while aboard an airplane. "We were supposed to take the baby to the bathroom, but we thought we could do it really fast on the chair," Ross recalled. "We were trying to be sneaky, but the stewardess was like, 'I'm sorry, but people are really unhappy about the fact that you're [changing her diaper here].'"
Looking back, the Ashlee Simpson Show alum realizes their mistake. "She was such a little baby. I didn't want to have to go in [the bathroom]. She was like 4 months old," she told Us. "But no, it really isn't OK and I do know that, but my sneakiness was really embarrassing. It wasn't so sneaky."
The couple, who wed in 2014, were afraid of potentially exposing Jagger to germs in the restroom. "Bathrooms on the plane are so small. Where are you supposed to change a baby? ... We were looking out for us," Ross explained. Simpson added, "You don't want your kid to get sick!"
Embarrassing moments aside, Bronx and Jagger get along swimmingly. Like their parents, the kids are both into music. "He likes to write songs and she's into singing Moana right now. She also loves Mama D," Simpson told Us, referring to her husband's mother, music icon Diana Ross.
And while parenting keeps the singers busy, they're also working on an album together and thinking about a possible joint tour. "It's been incredible and we're taking our time, but very soon you'll be hearing something," Evan told Us. "We're making this music inspired by our love and also our life."
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