Jennifer Garner has been a mom for a while, so she knows a thing or two about how sneaky kids can be. She said as much to Jimmy Fallon on Tuesday night, when she stopped by the Tonight Show and he asked for parenting advice.

Fallon, who has two young daughters now, said that Garner had given him good advice in the past and asked for more gems of wisdom. Fallon says that his 19-month old, Winnie, loves her 3-month old sister and wants to give her kisses as often as she can, but Garner says he should take lots of pictures of the sweet moments, because down the road they get few and far between.

“You know, they have their moments… You’re driving to school and you kind of hear a yelp. You look in the rearview mirror and there’s just like a pinch happening — a pinch for the ages,” Garner said.

Jennifer said that one of her daughters would outsmart her at times by reverting back to the baby of the family role without mentioning it.

“She wanted to be carried everywhere. What she was telling us was that she was a mermaid. She had a tail and she had flippers and she needed to be carried everywhere, and we bought it. Suddenly I’m lugging this huge kid around and I saw her smiling to herself, smirking… We would get to a staircase and she’d say, ‘Oh my tail, what with my flippers, I can’t make it up that staircase.’ We’re just totally going along with it… method, for sure. They’re smarter than you are so just be ready for that.”

Family means a lot to Garner, who is married to actor Ben Affleck; the actress told Savannah Guthrie on the Today show earlier this week that she was so excited to do a photo shoot for Southern Living Magazine with her mom and sisters, and became choked up while talking about it.

“There’s just nothing like sharing the spotlight with your sisters and your mom,” she said. “It’s always fun for me to get my sisters dolled up and my mom… I can’t even take it.”

Jennifer opened up about her close relationship with her family and said that her role within the Garners is the thing that defines her most.

“Being the middle sister of these three girls is the relationship that defines me more than anything else. More than being my kids’ mother, more than being my husband’s wife, I’m first and foremost the middle Garner girl.”