Hold the Power button down for 20 seconds then release. Press the Power button again for 2-3 seconds to restart the device.
If the Power button method doesn't work, allow the battery to fully discharge and then recharge the device overnight as doing so may allow the device to recover if it's stuck in an active state (e.g., screen on, playing audio, web browsing, etc.)
Look carefully for cracks in the front glass. Any cracks is the glass can lead to erratic touchscreen behavior.
Ensure the device has the latest software version installed. To check for software updates, refer to Install System Updates - Ellipsis Kids.