In this shot it shows Daniel on the train with HW, and HW is pawing at Daniel's face. In this scene you see Daniel crack a smile which shows, mainly, that he does care for the child. It is also the realization that this could be Daniel's successor, as he has no siblings, seemingly, and no hints or traces of a family. It will be explained later why Daniel will never have a wife. Aside from that, HW is his family business. It is on the train where you hear the beginning of Daniel Plainview's speech to a local town about drilling for oil on their land. The speech is first audible in the train because he knows HW will be good for the marketing, everyone likes a family man.
The key is that he does express genuine feelings for the child in this scene, so it plays both ways.
