Letters BIG and letters small

Last night I was reading to Logan.... ah, no. We have to change that. From now on, it must be "...Logan and I were reading..." because that's what it has become. A cooperative effort. Last night Logan and I were reading Richard Scarry's ABC book and after we finished and before I could slam the book closed, he noticed that on the endpapers are the letters of the alphabet in their capital and lowercase versions. I was explaining to Logan that "A" and "a" were the same letter, just written differently for different reasons that I didn't even want to try to get into, but he kept asking why and so I started talking about sentences and proper nouns and then Logan, tired of my ineffectual attempts summarized for me: oh, the "A" is the mommy A and the "a" is the baby a. The "B" is the mommy B and the "b" is the baby b, and .... all the way to Z and z, and then I bid him good night with a kiss and wished him many, many ZZZZZZZZZZ and zzzzzzzzzzz on his way to dreamland.