Fledgling magpie stuck in garden

I have a magpie fledgling in my garden. It seems to be limping, trying to fly off but every time it tries ends up falling over on to the ground. No sign of parents at all and been monitoring since early this morning. Keeps opening its beak wide looking for food.

I do not know where it has come from as I have no trees in the garden. 

Have put a water source out for it with it being warm weather but not gone near it. 

Any suggestions on what I should do if anything?