My own opinion is that it is entirely reasonable to buy a simple/cheap pushchair. A day is a day and it is not reasonable to expect you to manage without it. And you do not know how long they will take to deliver it to your hotel. I have given this advice before and been flamed for it - always travel with a cheap pushchair/pram that you don't mind losing. I am sure BA will not refuse a claim for a €30 pushchair and it is not too painful even if they did.