Saw one today and was very pleased. So I thought I'd post about them for other misinformed people / lurkers.
I got chatting to the lady pushing and her delightful son aged fourteen who was sitting in a really comfortable-looking seat in front. Apparently (this is a Tesco Extra though) they have three and you just request one at customer services.
We are finding that DS (4) is getting a bit snug on the trolley seat these days (although this is a good thing in many respects
) so I was really happy to see that there is an alternative to leaving him at home.
I might write a nice email to a big company for once in order to thank them and see if they could be more widely publicised.