I just want to draw your attention to what is quite simply the best article I've ever read on Low Muscle Tone in Aspergers Children;
Low Muscle Tone and Motor Clumsiness in Aspergers Children
The article covers detection of low muscle tone (or hypotonia to give its "proper" name), how it presents, exercises that you can do with babies and age-specific exercises you can do with older children.
It covers a wide range of topics from motor clumsiness to handwriting, grasp and balance problems. It even looks at the social implications.
It's well worth a read.