This Moose belongs to Me By Oliver Jeffers is  a fun book about a young boy Wilfred who finds a moose.  Wilfred names the mouse Marcel and gives him the rules for being a good pet.  One day when in the woods Wilfred discovers that another lady thinks that she owns the moose and she call him Rodrigo.  Very upset Wilfred runs into the woods and becomes tangled in his string.  As it gets dark Wilfred is getting very nervous being in the woods alone.  Then suddenly Marcel finds him in the woods and rescues him.  It is then that Wilfred decides he really didn't own the moose anyway.
This would be a great book to read to younger children and discuss just because you find something that doesn't mean it belongs to you.