This comes from a stupid game from when he guest-hosted the Ellen show, but she lifts it to new levels. It's called, "You Bet Your Daughter." The rules are too convoluted to explain here, but she does a passable job on the video. I'll just note that she's teamed with her mother (who bets on her daughter Kristen), and the other team is Jamie Foxx, who bets on his daughter Corinne.
I'm not sure if there are many star actresses who who put themselves through what Bell does here, or react as openly as she does.
By the way, a good friend of mine has directed Kristen Bell a lot on TV, and has stayed in touch with her over the years. And he says this is her, that she's just adorable and lovely.
P.S. To give some points to Jamie Foxx here, note that around the 2:05 mark, when it appears his daughter might be falling (yes, I know, but it's part of the game, you'll see...), if you look closely at him in the background you'll see him take some reflexive Dad Steps to catch her, before he realizes it's not necessary.