Originally Posted by Ldnn1

There is no 'wandering around' airside between terminals at LHR (at least not since T1 was closed) and you certainly don't want the faff of going landside with your kids, so just go through Flight Connections and stick in T3. No passport control, but you'll have to go through security so be aware of the liquid rules.

I haven't tried the PP lounges in T3 but both the Aspire and No1 are apparently pretty good. You can find reviews of both (and indeed all other UK paid lounges) over on headforpoints: https://www.headforpoints.com/2016/1...ow-terminal-3/. (My experiences of No1 at LGW and Aspire at LTN are also very good.)

Cabin baggage limits will be the same for the flight to BCN, but there is a very good chance your bags will be checked at the gate if the flight is busy. With young kids you should be first to board though so that may help.

I don't know about PP lounge options at MIA. BA uses concourse E but presumably you are travelling onwards with AA.