Probably the most important theme in Stuart Little deals with acceptance of diversity. Stuart and his family learn how to adapt to each other's differences and come to each other's aid when it is needed in order to cope with a particular situation.
To get to the washbasin, Stuart had to climb a tiny rope ladder which his father had fixed for him...For such a small fellow, turning the water on was quite a problem. He had discussed it with his father one day..."Maybe I could pound the faucet with something and turn it on that way," he said. So Stuart's father provided him with a very small, light hammer made of wood; and Stuart found that by...letting it come down with a crash against the handle of the faucet, he could start a thin stream of water flowing...
Closely related, a second theme has to do with the virtues of adaptability and flexibility. Stuart's size presented challenges at times but could also be used to advantage.
When the bus came into view, all the men waved their canes and brief cases at the driver, and Stuart waved his spyglass. Then, knowing that the step of the bus would be too high for him, Stuart seized hold of the cuff of a gentleman's pants and was swung aboard without any trouble or inconvenience whatever.
The third major theme highlights the joys of undertaking adventures. Stuart discovers a whole world of beauty and new experiences when he leaves home to search for his beloved friend Margalo.
In the loveliest town of all,...Stuart stopped to get a drink of sarsaparilla....It seemed to him a place he would gladly spend the rest of his life in,... if it weren't for the fact that something deep inside him made him want to find Margalo.