manipulation

At what age will the manipulation stop?
The bedtime conversation tonight went as follows:
Jayce: "Daddy I need my milk, STRAWBERRY milk".
Keith: "Jayce no strawberry milk at night, we have COWS milk at nighttime...it is really yummy."
Jayce: "But I really want STRAWBERRY milk".
Daddy: "But COWS milk is better."
Jayce: "Mommy, daddy gave me cows milk but I really wanted strawberry milk."