I would book one adult and kid into 2F and then another 1J and then wait for F to open up.
I have done 4 F last December during Christmas (JFK-HKG) I booked 1F1J and then 1F3J and eventually moved to 4F two days before departure. With AA I had no problem with changes but ended up paying over 200 for BA bookings. Paid some change fees with Citi thank you cards and got 34K flight points too.