I assumed the dinner itself would be the mom and dad already aware Sakura and Kakashi are dating. I don't think Sakura would slip up and try to feed him though, she'd be trying to behave and prove it's not some silly fling or crush and that to me, would mean being polite but also sincere and on good behavior. ^^ Probably after they eat, she'd like to hold Kakashi's hand as they have tea and dessert.