What happened to my wee boy?

My mate Blair is over for a few beers and some dinner tonight - we went through to visit my Gran first - according to her, she and Blair are 'on the same wavelength'.

I picked up Blair from his mum and dad's house and couldn't resist taking a picture of this very embarassing picture of him and his sister. Here's the then and now comparison.

What happened?

PS. I particularly like the library background used on the childhood picture.