“What about Mama? Will you call her Mom? Billy nodded slowly. “We can tell her together when she comes home from school.? They fell silent. Billy chose another cookie and bit into it. He looked at Papa, taking him in. It was strange—Billy wanted to call him Dad, but he still thought of him as Papa.
The above paragraph is from The Year of Billy Miller on page 96. I am not very sure the meaning of 'take him in' in the bold sentence. There are two explanations on Thefreedictionary.com, to cheat or deceive someone and to give shelter to someone. But I don't think these two explanations are good enough to explain the meaning of the sentence.
Personally, I think 'take him in' here is to emphasize the way that the boy, Billy, looked at his father, which means he looked his father and brought his father's image into his mind.
Am I right?