Erin and Sara Foster's Quotes About Relationship With Katharine McPhee
Katharine McPhee may be younger than her stepdaughters Erin Foster and Sara Foster, but they still have a close bond.
The American Idol alum started dating David Fosterin 2017, and the pair got engaged one year later. In June 2019, they tied the knot in London. News broke in October 2020 that McPhee was pregnant, and baby boy Rennie arrived in February 2021.
Throughout their relationship, David and McPhee have gotten backlash for their 35-year age gap. However, his kids are not pressed.
"Everyone has an opinion about something," Sara said during a June 2026 appearance on Kristin Cavallari's "Let's Be Honest" podcast. "They're 12 years in, and they are happy. … She's a fully consenting lady, this is not, like, some child bride. She is in her 40s."
David is the father of six kids, including Rennie. His eldest daughter, Allison, was put up for adoption following her birth and reconnected with her father in adulthood. He shares daughter Amy with ex-wife B.J. Cook and three kids - Sara, Erin and Jordan - with ex-wife Rebecca Dyer.
Keep scrolling to see what Erin and Sara have said about McPhee:
July 2018
Following her dad's proposal, Sara called McPhee "Mommmyyy" via Instagram.
September 2018
The siblings joked exclusively to Us that they "hope[d]" they'd get invites to their dad's nuptials.
David "never looked better" while dating McPhee, Sara exclusively told Us. "He's so happy," she explained. "He doesn't age. I said to him the other day, I'm like, ‘Are you on HGH? What is happening?' He just looks so young." Erin joked at the time that his "young fiancée" should take full credit.
February 2019
Sara called her future stepmom "really funny," exclusively telling Us, "Katharine holds her tongue a lot. If I were her, I would be taking down trolls all day. I wouldn't be able to star on Broadway because I'd be too busy taking down trolls."
Amid rumors of McPhee and David spending millions on their wedding, Erin joked via Instagram: "There goes my inheritance."
May 2019
"We love our future stepmom," Sara exclusively told Us. "Our dad's very happy and we're excited."
August 2019
The sisters said during an event that they "fully expect [McPhee] to have a child and fully support it." (McPhee welcomed son Rennie with David in February 2021.)
September 2019
"The truth is we really genuinely love Katharine," Erin exclusively told Us. "It takes a very strong, graceful person to come into a family as the fifth wife and have adult daughters who are older than her and do it in a way that really creates inclusion with the family, and she just does it effortlessly. She just makes it really easy for all of us to get along. So we're very grateful for her."
October 2019
Sara clarified exclusively to Us that McPhee wasn't pregnant yet, saying, "Of course she wants a baby. I'm sure they'll have a baby."
November 2019
She called her dad and McPhee the "perfect couple" at an event, exclusively tellingUs Weekly, "I don't think they've ever had a fight. I watch them, I'm just like, they figured it out. It's beautiful."
April 2021
"You ever side-planked with your 37-year-old stepmom?" Erin wrote on her Instagram Story. "I have."
May 2021
"Happy first mama's day to Rennie's mom," Sara captioned an Instagram Story shot.
July 2021
Erin compared her and Katharine's July 2021 workout with Amanda Kloots to "death."
December 2021
"If I can accept my stepmom looking like this, you certainly should be able to," Erin commented on an Instagram upload showing McPhee's post-baby bikini body. "The photo [my dad posted of her] wasn't altered or filtered, and she's had no surgery. You can't shame someone for feeling cute after a baby whether she's sharing stretch marks or a six pack. Let her live."
July 2022
Erin trolled her stepmom via Instagram after she posted a PDA-filled snap with David. "Poor guy … too bad he doesn't get very much attention," McPhee captioned the sexy snaps, to which Erin replied, "Reporting this."
December 2022
Erin showed the "My Grown-Up Christmas List" singer support - and praised her saucy style - after seeing McPhee's green Vegas gown. "Okkkkkkkk 🔥," the TV writer commented via Instagram.
February 2023
After McPhee shared a series of throwback photos of her life with David via social media, Erin was quick to respond. "It was always you. Happy 💕 day," the Smash alum captioned the Valentine's Day post, to which Erin wrote, "😭😭❤️❤️."
June 2026
Sara slammed critics of David and McPhee's age gap, praising her "amazing" stepmom.
"I think it's hard being a stepparent, obviously. I think you want to ride the line of wanting your partner's kids to like you and wanting to show up as a motherly figure," Sara said. "But you also have to have respect for the real mom … the biological mom."
She added, "I think it's a tough balance, and I think she does it really well."
July 2026
Sara called McPhee "fantastic" on "The Morgan Stewart Show" podcast.
"She's so gorgeous, and I'm so obsessed with her," Sara said. "She taught my 10-year-old how to ride a bike."
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This story was originally published July 1, 2026 at 2:25 PM.