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 Aimact
Targus AMB582GL mouse Right-hand RF Wireless + Bluetooth Optical 2400 DPI
ShopBetter24
Wireless Mouse Targus AMB582GL Black 2400 dpi
This product is also available at 1 unverified merchant.