It is said that it is Sabrina's 16th birthday. It is also said that she is starting High School as a Freshman that day. In the show both of these facts are true, but in reality most people are Juniors and at their third year of High School at 16 or 17, and Freshman start their first year at High School they are 14 or 15.
Sabrina is served a huge stack of pancakes for breakfast. The Spellman family cannot eat pancakes due to developing an instant addiction to them which Hilda and Zelda would be well aware of.