After studying these annoying girls carefully (and reading what everyone else thinks), I'm going "fake".
1. At the :43 second mark, her head is lifted up doesn't fall back into the cake when released.
2. There is a countdown before the singing which is something you really wouldn't do with a crowd of three
3. The kid eating the cake in the midst of the chaos is just something some scheming girls would script to give a video that extra viral factor.
4. A split second before the birthday girl has her face spiked into the cake, she takes a deep breath.