Your young maple has winter injury.  Thin barked trees, like maples, need to be protected by white tree wrapping for at least the first five years.  The winter sun heats the bark, which expands.  Then the nights get cold and the bark shrinks.  This process eventually causes the crack you see on your tree. You cannot fix it but can prevent further damage by wrapping the trunk all the way up the the lower branches in October.  Remove the wrapping April 1st or so.