Playing Library

Last night, Ian and I were playing before bed. Well, actually I was reading a book. Ian started taking the books and holding one out and said "Beep." And then took another one and did the same thing. It took several times of him doing this for me to notice and realize what he was doing. I said, "Are you playing library, checking the books out?" He said yes and continued, with the same books over and over, saying "Beep" and "Playing library." He actually says li-li.