How to describe this tone when conversing with a child?

I'm looking for a way to describe how, for example, an adult might respond to a child in this situation: A parent asks his young daughter what she learned in school today, and the child excitedly begins telling the parent all about her lessons. The child speaks as if she's enlightening the parent with new and intriguing information, when in fact the parent is certainly knowledgeable about everything his daughter is describing. But the parent listens attentively and feigns that he find the information new and fascinating.

The parent isn't patronizing his child. He's showing kindness, not condescension. Encouraging doesn't seem quite right, either; yes, the father is trying to be encouraging to his daughter, but in an indirect way. You couldn't say the tone itself was encouraging, per say.

If the child were old enough to pick up on the fact that her parent was obviously pretending not to know what she was discussing, you could say he was being playfully sarcastic. But that isn't what I'm trying to convey.

Thanks in advance for any help!

Edit: Based on some of the responses, allow me to clarify that I don't mean to suggest the parent is pretending to be interested with the actual conversation itself, only that he is letting the child continue as if he doesn't know anything about the subject matter.

I would describe the parent's attitude in this scenario as "solicitous", which is defined by oxforddictionaries.com as "characterized by or showing interest or concern".

I go through this everyday with my young children. Every afternoon, they're bursting with excitement to share their newfound knowledge (from pre-school and kindergarten).

I'm happy to entertain their enthusiastic explanations despite already being familiar with the subject matter because I want to build their self-confidence, convey my approval, and, most importantly, be:

supportive

So during their talk I would say my tone is always and mostly supportive.

The parent is interacting with and letting their child learn to communicate.

A consciencious parent knows how important this developmental phase is and will be not only patient but also really interested in what their child has to say. The parent doesn't have to pretend not to know whatever the child is talking about, they show they are interested and may even correct one piece of information that the child may have misunderstood. And take my word, their fascination will be real, not feigned.

The parent is identifying with their child.

From McGraw-Hill Dictionary of American Idioms and Phrasal Verb:

identify (oneself) with someone or something:

... to relate to someone or something;

and from Thesaurus.com:

identify with verb

put oneself in the place of another