Before we have language, we have acting. A very young child will often reenact part of the action in order to communicate. To get mom to blow a bubble, the child might blow while looking at mom--perhaps with one hand up as though holding the bubble wand. A child with autism, learning language much later, might continue to use this reenactment method of communication but find it hard while blowing to simultaneously look at mom and gesture as though holding the bubble wand. The child might have been communicating but it would take a very observant mom to know that the message was blow another bubble. Many moms and dads are just this observant, however. Parents serve as interpreter for their child in my therapy sessions all the time and I hate to think of how much child communication I would miss without the parent there. .
Sometimes we mistakenly think that a child is engaged in a self-stimulation/regulatory behavior as we watch the child move his hands in front of his face. The mother of one of my clients pointed this out to me today when she said that sometimes her son was just flapping (a self-stimulation/regulatory behavior) but at other times he was reenacting the movement of something that interested him, like the clock on the clock tower as he heard the bells ring. He might reenact the clock movement even if no one is around because he wants to think about what he just heard and he does not have the language skills to tell himself, silently in his head, that the bell sounds in the clock tower. Thus, he tells himself what that sound is by reenacting a clock. This is self-talk, which is a very important skill for a child to develop. Think about how much dialog is going on in your own head as you try to decide what next to do, think about things you have done, and talk yourself into and out of behaviors that would or would not be wise. Reenactment is just one of the strategies that a child might use to try to cope with delay in language development, but it is an important strategy.