More so than any other festival, the Seder-night is dedicated to children, because the Torah dictates that we must tell the history of the Exodus to our children on this night. The Haggada directs us to do many unusual things to arouse the children's curiosity so that they will want to know "why this night is different than all other nights."
Immediately following Kiddush the curiosities begin. We wash hands as on each Shabbat or Festival, but on Seder-night we wash without a blessing because we first eat karpas (a vegetable) and not bread. Just as karpas whets our appetites for the matzah, so too, this unusual procedure interests us in the secrets of this night.
The four questions expressing the childrens' interest are more than just a springboard for our discussion. They are part of the answer - the best story is one you want to hear! That is why the Sages say that even if you sit by yourself on this night you should interest yourself in the material by asking the four questions. People are inquisitive and should not be afraid to ask; if you are embarrassed to ask, you do not learn. The custom of providing treats for the children not only helps keep them awake, but also serves as a stimulus for their questions, and as a reward for their participation.