One of my next gen OC’s, a Pinkie kid! =P

Surprise Party is Pinkie Pie and Cheese Sandwich’s daughter. (Little sister to “Lil Cheese” in my headcanon. Whom then gets known as “The Big Cheese” after her birth. Also, my personal headcanon.)
A pegasus born to two Earth Ponies…was indeed a surprise, but, lets face it. Its a Pinkie kid. lol.
(In my headcanon, the original Surprise pony is Pinkie Pie’s Great-great-great-great…ect ect, Grandmother. Thus, Surprise ends up getting a lot of those traits quite randomly from the gene pool, down to her coat being a much softer pink/peach color, and the blonde in her hair.)

So, with her race being a surprise to the two of them, they had a chance to name her after one of their most favorite things in the world. Surprise Party. (Unknowingly, naming her after her grandmother.)

She takes after both her parents, and wants to grow up to follow the legacy of the party pony.

(I also like to believe she tries her hardest to be best friends with Morning Star, before he turns into “Mourning” Star. Maybe she even has a little crush on the moody unicorn boy? If only he knew she would give him her wings if she could.)