Ben and Isabella just stood there, stunned.

Dang - their little brother was straight-up adorable when he smiled. Total heartbreaker in the making.

Isabella couldn't resist going for those cheeks, but Sam saw it coming a mile away and ducked.

Nuh-uh - in Sam's book, little sisters don't get cheek-pinching privileges.

So what does he do? Turns the tables and gives her cheek a playful pinch, complete with silent ...