I had exactly the same thing happen to a pair I'd bought ds
I was a skint single mum,but invested in shoes for the kids
I bought a pair for him in the sale and he'd worn them 3 times over 4 days (just trips to the corner shop,a walk to his grandparents about 1/2 a mile away and a trip into city centre)
He was stood next to me,wearing them while in the city centre and we went to walk away when the whole sole fell off
We where round the corner to the shop I'd bought them from,(coppergate branch in york-i moved away 8 years ago so dont know if its still there) so took him in (with the receipt that was still in my purse) and the same sales assistant that had sold me them,yelled at me 'what do you expect?they are SALE shoes!'
Busy Saturday afternoon-everyone who was in the shop heard her and ds burst into tears thinking it was his fault
She refused to swop them for another pair or a refund (she just kept screaming about them being sale shoes) and I got nowhere with head office-they just brushed me away
£30 is a lot of money when you've saved so hard in the first place
I'd never go back to them-i found next where ace for boys shoes and asda for girls (but it's been a while since I've bought children's shoes)