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Thanks for all your responses.
I'm not sure who it was who asked us to leave, she could've been a manager but didn't introduce herself as such. I was so embarrassed, I just picked up our bags and left. The temporary barrier was basically just a rope barrier with metal stands which they take in at closing time - if the pushchair had been on the other side of the rope, we probably could've stayed.
I'm just surpried by it all, there was nothing to say that kids weren't welcome, and if we were indoors then I would've said fair enough, as I know that its up to the landlord who to admit or not, but since they don't own the pavement and my daughter wasn't using their furniture or having anthng to eat or drink, but was accompanied by 2 paying customers intending to have a meal, I think their descision was odd (given the current finacial climate) and wrong, but who am I to argue?!