*up* to to 500mA is the spec. Don't know about Toys USB port current capacity.
*Many* USB hard drives need close to 1000mA to work (they'll often light up but not spinup with one port), which is why they often come with double USB pigtails. In your case, the drive will probably need a separate power connection + USB connection, if the issue is power related.
The Toy head unit may also not be waiting for the hard drive to spin up and become "ready", even if it would operate from one port and getting sufficient current.