Under The Greenwood Tree is opposite The Frog pub and the Sainsbury's Local, not far from Old Town Library:
http://www.underthegreenwoodtree.co.uk/
It's an absolutely beautiful shop full of gorgeous stuff and the staff are SO friendly, they can't do enough for you. Every time I've been there, my son has had a good go at trashing the place, and they don't mind in the slightest - in fact, they offer to hold him for a while and find new toys for him etc.