It is rude to favor one kid over another.
Stanley has 2 children who are interested in getting better at tennis, but one is clearly more talented than the other.
Stanley wants to maximize his kids' ability.
Stanley makes sure to split his time between both kids and pay for lessons when needed, so they get as much practice as possible.
Stanley spends a lot more time with the more talented child and pays more more lessons for them.
One kid improves quicker than the other, but they both practice hard and enjoy improving their abilities.
The more talented child improves quickly and makes their school team, but the other feels neglected and starts to feel depressed.