Assuming that you would not require an extra seat for the then two month old, I'd the following:
a. WTP + MFU (40,000 miles if i recall correctly) for upgrade to CW for 6yold
b. companion ticket for you and Mrs.
BTW, if you book today, you would need to make BA aware that you will be travelling with not-yet-born infant in order not to incur change fees / hassle later.