In which format are you scanning them to? Usually your scanning software allows you to select a format (e.g. JPG, PNG, GIF, TIFF). I'm thinking you are scanning them as TIFF, which is a large file size.

Also, do you know what resolution you are using? The larger the numbers, the larger the actual file and image size.

Feel free to take a screenshot of your scanning utility, and we can provide additional guidance!