There's no one answer for this. If it's small/the cabin crew are in a good mood/the gate staff aren't being anal/the planets are aligned in your favour, you might be lucky.

BA will not however recover buggies from the hold at LHR and deliver plane-side, so if it goes at GLA then check where they tag it to!

Personally I would be more concerned about the interminable wait at Miami Immigration and not having a buggy there!

Also note that the CCR doesn't have a kids playroom, but the First lounge does. You can move between the two easily enough though. Also, I thought the signing for this in the First lounge was terrible, but if you head towards the refectory, the play area is on the right. Has a TV with C-Beebies on it, plus some big soft shapes for toddlers to clamber over.

How old is the infant? I have seen a buggy that folds down to just 18 inches so would be well within the allowed limits - our Quinny Zapp is over, BA have however been fine with us putting it onboard widebodies and also into Club Europe.