It's good that he's agreeing. Leo lets him eat his ice cream, licking on his own, and heads for the library.

By the time they will likely be very sticky. Once that ice cream starts melting, Leo can just see it dripping onto his hoodie. Oh well, at least Donnie is content.

Once they get to the building, Leo sweeps his hand at it and says, "Here it is! The library! Woo!"

He may not get excited about the library on his own, but he does want to see little Donnie's reaction to it.