Hilary Duff's Mischievous Son Luca Gets Haylie Duff's Daughter Ryan Into Trouble: See the Cute Moment!

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What are cousins for if not to get into a little trouble?

Haylie Duff posted an adorable pic of her 2-year-old daughter, Ryan, posing on the hood of a car with sister Hilary’s son, Luca, on Monday.

WATCH: Hilary Duff Shares the First Present Her Son Ever Picked Out For Her

But don’t be fooled by those innocent smiles! Turns out 5-year-old mischief-maker Luca was teaching little Ryan how to climb onto cars.

“This is AFTER Luca taught her to scale to the top of @hilaryduff car!” Haylie, 32, captioned the cute snap. “?❤️ These like cousins are gonna be trouble ?‍♀️ #HerIdol #WantsToBeJustLikeHim.”

Hilary, 29, later reposted the pic with an apology for her sister.

“Cousins stick together,” she wrote. “Dubs trubs @haylieduff I'm apologizing on Luca's behalf for teaching that angel of yours that it's cool to climb on cars ?.”

In March, Hilary opened up about co-parenting with her ex-husband, Mike Comrie. The pair finalized their divorce last year, following six years of marriage.

WATCH: Hilary Duff Says Being Divorced ‘Sucks’

“Some of my friends tell me, 'God, it must be so nice, you get a break from your kid because you share him,'” she told Redbook magazine. “I'm divorced, and it sucks. Well, it did suck for a while; now it's just normal. But it's true, I do get a break.”

See more on the Younger star below.

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