I tried looking at the user manual from their main website: Sprout Channel Cubby
However, I had an error with viewing the pdf file. I agree with B. Diddy: try holding the reset button for a few seconds. It may be set up like that to ensure that a reset is intended.
Try "Settings", "Backup and reset". Evidently the "reset" button is just a hard CPU reset. (It pulls the CPU reset pin to ground, to make it restart, but it doesn't wipe all the data, the way Androids normally do - a good safety feature on a tablet made for kids.)