If you want full freedom of movement, you should opt for a wireless mouse such as this one. Children, or adults with smaller hands, might find that this mouse works well for them.
From Amazon
Trust Yvi FX Wireless Mouse with LED Illumination, USB Micro Receiver, RF 2.4 GHz, 800/1600 DPI, Ambidextrous, 8 m Range, Computer Mouse for PC, Laptop and Mac - Black [Amazon Exclusive]
Conrad Electronic
Trust Yvi FX Mouse Radio Optical White 4 Buttons 1600 dpi
OnBuy
Trust Yvi FX mouse Ambidextrous RF Wireless Optical 1600 DPI