What's Up With No Cell Phones in Kids Books?

On about our 20th reading of Llama Llama Red Pajama, it struck me that Mama Llama was doing dishes while talking on a slimline, wall-mounted, spiral corded phone, and I wondered if my kid even knew what that was. I asked, she shrugged her shoulders, which could have meant "no" or could have meant "I'm not a trained monkey ... keep reading!" Later, I flipped back to see when it was published, 2005. Christ, even my in-laws had upgraded to a cordless by then. That's when I started seeing dated tec