I second the Clarks suggestion, if you can get to a Clarks at the weekend. You probably could order online, but it's better if they fit them. The Clarks fitters are usually great with kids, shoes are cute and hardwearing (both soft-soled and hard-soled), and hopefully don't break the bank. I've heard good things about John Lewis for kids' shoes, but never been there myself.

By the way, we have these and are very happy with them:

http://www.clarks.co.uk/find/EndUses-is-cruising/Tube-is-boyssport-or-boys/product-is-20332310