+1 for having the kids flying Y - although I do not mean to judge anyone, I always felt flying kids around in J/F does not send the right message, especially if on hols.
Also, not to kill the dream but you are not missing much if you are not allowed in the CW Galleries lounges. IMO only F and above are worth a stay in LHR.
That said, if lounging has to be part of your departure experience, you can consider buying entrance to the paid lounge at T5.