If USB Digital Microscope with 400 times magnify capability not enough for you may consider AmScope, the all-metal cordless LED Student Compound Microscope. Unlike USB Digital Microscope that only offered one magnify capability. This device comes with five magnification setting (40X, 100X, 250X, 400X and 1000X).
The AmScope features 360 degrees rotatable Monocular with five magnifications setting up to 1000X with a640x480 pixel USB 2.0 Imager, view and/or capture snapshot images or video to your computer, coaxial coarse fine focus, single lens condenser with disc diaphragm, LED illumination system that can be powered either wall-power or three AA batteries (or rechargeable batteries), and sturdy all-metal framework.
The AmScope 40X-1000X cordless LED Student Compound Microscope comes with a camera that can be used to replace the microscope eyepiece so you can view comfortably on your computer screen using their included software. It is compatible with Windows XP, Vista, and Windows 7 operating systems. This cordless microscope is ideal for use at home or school uses for students from elementary to high school.
If you need one for your children, you can buy it from Amazon.com for $119.98.