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Mama's got jokes!

In this sneak peek from tonight's all-new episode of Eric & Jessie, Jessie James Decker hilariously warns her expectant sister, Sydney Rae Bass, about the "joys" of pregnancy as they hit the pool in Las Vegas with their BFF and Jessie's stylist, Jessica Payne.

As the girls strip down to their bikinis, the country singer just can't believe the size of her little sister's breasts. "Your boobs are ginormous," she tells Sydney. "I think your boobs are going to be bigger than mine got. I mean, I got to a 32G."

"They're already massive!" Sydney says. "They've already grown two cup sizes and that was in three months."

"Imagine how much bigger they're going to get when they get milk in there," Jessie says. "That is when it's, like, overwhelming."

The mom of two then goes into detail about the body changes she experienced during her pregnancies with daughter Vivianne Rose Decker, 3, and son Eric Decker Jr., 2.

"It was seriously like someone had put two melons in pantyhose and then plopped them in and they just hung out at the bottom and then tied them to your chest," she explains to Sydney, laughing. "That's what my boobs were like. Whenever I would go up and down the stairs, they would slap on my stomach."

She jokes, "So, that's what you have to look forward to." LOL!

Meanwhile, the "Lights Down Low" songstress also considers what to tell her children about sex when they're older.

Find out what she decides in the clip above!

Watch a brand new episode of Eric & Jessie Wednesday at 10 p.m., only on E!