Carrie Underwood tells PEOPLE for this week's issue about the heartwarming time her 3-year-old son Isaiah "made [her] feel pretty"
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Need evidence of Carrie Underwood‘s beauty, both inside and out? Just ask her son.

The country star spoke to PEOPLE for this week’s issue about her CALIA active wear line and a recent incident where her only child, 3-year-old Isaiah Michael, made her “feel pretty” when she wasn’t quite feeling it herself.

“I feel the prettiest when my kid says something that’s just super sweet,” says the “Cry Pretty” singer, 35. “This morning, Melissa, my hair and makeup artist, was starting to put my makeup on and he’s all in his pajamas and he said, ‘No, don’t do that!’ and I was like, ‘Why, baby, why are you upset?’ ”

“And he said, ‘I like you just how you are.’ He didn’t want me to put makeup on,” explains Underwood, who received 40 to 50 stitches in her face after a scary fall last November.

“That made me feel pretty. I know I wasn’t [pretty] because I had just woken up and hadn’t brushed my teeth yet, but he made me feel pretty.”

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Underwood is committed to a healthy lifestyle, telling PEOPLE she and husband Mike Fisher don’t keep soda in the house because they “don’t want Isaiah to have it.”

“He doesn’t eat a lot of red meat, my husband doesn’t eat any and I certainly don’t eat any. Stuff like that, we stay light on,” she says. “We don’t have a lot of potato chips. We’ll have veggie straws, which are really good, but are a little better than chips.”

“But some days, I’m like, ‘Kid, have your ice cream. Eat your pizza! This is the only time in your life you’ll be able to metabolize it. Enjoy it,’ ” the singer continues.

53rd Academy Of Country Music Awards - Backstage
Credit: Jason Merritt/ACMA2018/Getty

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And have the spouses of nearly eight years considered expanding their family further — more specifically, has Isaiah requested a sibling? “It seems like all my friends either just had a baby or are about to have a baby, so he’s surrounded by other people’s babies and he loves it,” she says of her son.

“My best friend just had her second little girl and I was talking to [Isaiah] and I said, ‘You know, you are going to have to take care of Leona and Ava,’ and he was like ‘Okay!’ ” Underwood shares. “He knows he’s their big brother.”

For more from Carrie Underwood, pick up the latest issue of PEOPLE, on newsstands Friday.