Driving in the car, talking to her cousin:
"I am going to have a birthday party. It's going to be barbies and princesses and butterflies. I will invite you. Everything will be pink and purple. Those are my favorite colors. I am going to have a biiiiiiiiiig cake and a bouncy house. It's going to be so cool. I am ALL about birthdays.
Her cousin just looked at her like she is crazy (he is a boy, obviously boy's aren't all about birthdays)
Her birthday is in January. She has a long time to plan this shindig.