Learning to talk is a gradual process. It's common for a child's speech to become less clear as she tries more words with more difficult sounds, because they require more effort and motor control.
Your child may in fact end up saying as little as possible during different stages of learning to talk, or he may begin to act up, out of his frustration at not being able to communicate the way he'd like.
Usually children's speech improves over time. But if you are concerned that your child's speech isn't improving or if your child keeps acting up, out of frustration over not being able to be understood, you may want to discuss this with your child's doctor or call the Canadian Association of Speech-Language Pathologists and Audiologists at 1-800-259-8519.