What to do about a fledgling wood pigeon?


I have wood pigeons nesting in my garden.  This year they have one chick, who is now quite big.  He's still mainly covered in fluff but about half the size of an adult.   I thought they had got used to me having a peek at the nest on my way past the tree - it is at head height.  But now realise I should have left them alone, as this morning I tried to lift my son up to show him and I must have frightened the Mum and she flew off.  I quickly left and saw her fly back to the tree, but maybe she didn't get back in the nest.

However, this evening when I went out to the bins, I saw she was not on her nest.  I waited til it got dark and checked again, but she's still not back.  The young pigeon looked hunched up and cold, and I thought about bringing him inside and putting him in a box, then trying to look after him, but having read on the websites, it seems it's best to leave him where he is.  If neither of the parents return and he looks worse, should I try to look after him or just leave him? How long should I give it?   I don't think he's ready to look after himself yet and I would hate to see him die.  I'm not able to drive at the moment, so can't take him to Tiggywinkles which is where I'd normally go. 

Any advice would be greatly appreciated.