This is one little step forward. Not as convenient as a 3d party child protection suite but better than handing a completely unprotected device to children.
Google also offers some help on their website: https://support.google.com/nexus/answer/3175031/?hl=en
Read the full article here: http://www.howtogeek.com/223530/how-to-lock-down-your-android-tablet-or-smartphone-for-kids/