Rabbi Hirsch Melech Shapiro (known for his sefer B'nai Yissoschor) writes a very fascinating idea in his sefer Derech Pekudecha. The Chumash records that Hakadosh Baruch Hu told Moshe Rabbeinu that He plans to bring about tremendous miracles in Mitzrayim in order that B'nai Yisroel should tell over these stories to their children and grandchildren so that they should know all about Hashem. It would appear in the Chumash that the main purpose of the mitzvah of sippur yetzi'as Mitzrayim on Pesach night is to convey to our children all of the principles of faith (i'karei ha'emunah) which were demonstrated through all of the eser makos. Although Hashem is invisible, after experiencing the eser makos first hand it became obvious and apparent that there is a G-d in the world. The Torah tells us also that Hashem caused all of the avodah zaras in Egypt to fall apart to demonstrate that there is only one G-d. There were always thinkers who philosophized and suggested that it is physically impossible for the Infinite G-d to communicate with finite man; they claim there cannot be such a thing as prophecy. However, the people realized that Moshe Rabbeinu was a navi.
Included in the ikar ha'emunah of nevuah is the concept of tefillah. Just as G-d can, has, and will communicate with man, so too can man communicate with G-d by davening. The Torah says that B'nai Yisroel prayed and Hashem answered their prayers and took them out of Egypt. There were always thinkers who philosophized that although there is a G-d who created the world, because there is no such thing as spontaneous generation so there must have been a G-d who brought life into existence, but clearly after He created the world, He no longer pays attention to petty things that go on in this world and does not really follow with anything that goes on in this earth. On the occasion of yetzi'as Mitzrayim it was clearly demonstrated that this is not so. The one and only G-d that created the world was fully aware of all that was happening. He punished the wicked and spared the righteous. The story of yetzi'as Mitzrayim demonstrated that there was clearly yedey'a (knowledge) of what was happening and also sechar v'onesh.
The entire Jewish nation heard both Moshe and Aharon deliver prophecies, but noticed that there was a stark difference between the two of them. Aharon's prophecies were all regarding horo'as sha'ah while those of Mosher Rabbeinu were sometimes dinim l'doros and sometimes horo'as sha'ah. The korban Pesach that was brought in Mitzrayim was a blend of dinim l'doros and horo'as sha'ah. When Hakadosh Baruch Hu instructed Moshe Rabbeinu to deliver the prophecy about the upcoming geulah, Moshe Rabbeinu says that when the people will ask me "what is His name, what should I answer"? Hashem gives a very cryptic response and reveals to Moshe Rabbeinu another one of His seven names (zayin sheimos sh'einom nimchokim): Eh'k'ye Asher Eh'k'ye. Rashi, quoting from the Midrash, interprets the meaning of this name / statement to be that Hashem will be with the Jewish people until ge'ulas Mitzrayim will be completed, and Hashem promises that He will again be with the Jewish people in the future during the long galus to bring about the ge'ulah ha'asida. Thus the ikar of be'as ha'Moshiach was also revealed right before yetzi'as Mitzrayim. It is for that reason that on Pesach night, at the conclusion of the seder, we all recite Nishmas Kol Chai, asking for that day to come soon when all of mankind will recognize Hakadosh Baruch Hu as the one and only ruler of the world.
However, the Moshiach will only come when all of mankind is willing to accept the malchus of Hakadosh Baruch Hu. There are many hard core atheists and ovdei avodah zarah who refuse to accept His malchus and because of whom the coming of Moshiach is being postponed. It is for that reason that we pray to Hakadosh Baruch Hu right before the conclusion of the Hallel on the seder night, "Shfoch chamoscha...", i.e. it is not fair that this group should hold back the coming of Moshiach. Wipe these people out and the rest of the nations of the world will be ready to accept your malchus. All of these principles of faith of our religion could easily be explained even to young children on Pesach night. According to the simple reading of the pesukim, it would appear that that is the main purpose and should be the main theme of sippur yetzi'as Mitzrayim.