If traveling with children in F, BA Flounge is probably a better option, as the kid's zone in T3 GF is fairly pristine (compared to BA's other kid's areas). From what I can tell, the CX F lounge does not have a kid's area.

Probably not a concern for most, but our plan for a few weeks from now (we're traveling with our 12, 9, and almost 3 y/o) is to settle into the F lounge area outside the kid's zone, take turns at the Elemis spa, and maybe move over to the CX F lounge for lunch before our flight to PHX if we're bored.