He's a smiley, giggly baby but reading development milestone charts (I know, I know...) gets me a bit paranoid. For example, he doesn't and never has put his arms out to be picked up. He has never copied noises or facial expressions. He is easy to get a laugh out of but isn't fussed about peekaboo or hiding games. It's the lack of imitation which really worries me. What does anyone else think? According to the books, he should have started basic forms of mimicry at 5 months old.