It is perfectly normal for young children to say some sounds wrong as they are learning to talk. For example, they might say "wabbit" instead of "rabbit." Having difficulty pronouncing words doesn't mean a child is less intelligent than other children - it usually just means he needs more practice talking.
Some sounds are more difficult than others and will take longer for a young child to learn. Easier sounds include m, p and d. Some harder sounds to learn are r, l, s and th. Don't forget that these few difficult sounds turn up in language often, so your child may sound worse than she really is.
Pronouncing things properly requires many precise movements of the tongue, lips and jaw. Your child will become better at making these movements as he grows and has more practice. It may take six to eight years before your child learns to say all the language sounds correctly.
If your child's speech is difficult to understand, please read the Related Content topics on Speech. For more information, contact the Canadian Association of Speech-Language Pathologists and Audiologists at 1-800-259-8519.