Some of us appreciate the fact that AA focuses its (admittedly imperfect) service efforts on all passengers, not just a coterie of people in a familial group.
If a family group feels it needs special attention, they are free to travel with nannies or other child care professionals.
And all members of a family seated in J or F are welcomed into LHR Arrivals (when opened). If a family chooses to seat some members in the main cabin, they are welcome to purchase an Arrivals pass for USD 90 + VAT for the Y passengers.