The haggadah speaks of 4 children asking about the seder[1]:

One child asks about the laws and all the details of halakhic observance. With this child, you can study all the laws related to Pesach and explain that they were designed to enable you to feel as someone who has personally experienced the Exodus, as taught in the Mishna: “In Every Generation, each person is obligated to see himself/herself as if he/she had personally left Mitzrayim” [2]. Remind this child that four times, it is repeated in Torah that you should not oppress the stranger, for strangers we were in the land of Egypt[3]; this is the founding theme of Judaism and this is where we should put the emphasis of our observance.

One child asks about what all these rituals mean to you. To this child, you can say, "what a great question! For me, one of the greatest aspects of the seder is that it has allowed me to experience liberation in many different forms. Sometimes, like Shmuel, I experience the seder as physical liberation; other times, like Rav, I experience it as  spiritual liberation; there are times I feel we are talking about civil rights in general and other times in which I am sure we are talking particularly about the Jewish condition throughout history. Every time, though, I experience the seder teaching me to fight oppression in all of its different forms. Now, tell me: what does this all mean to you?"

One child is naïve and has difficulty understanding why we are observing Passover if we are not slaves any more. To this child, you can explain that evil has existed in many different forms over time and our people has been a victim of evil several times in history. But evil also exists in ourselves, and sometimes we oppress others too, sometimes consciously, other unconsciously. Mitzrayim represents all these forms of oppression and the seder tells us to learn from the times we have been oppressed to understand how difficult it is to be in such a position. Our duty, therefore, is to fight oppression in all of its forms, including when we are the perpetrators.

One child does not know how to ask. You might start the conversation and make the story as interactive and interesting as you can to keep this child's attention. But  keep always in mind that oppression and liberation are serious themes, and that our redemption came at the price of human lives, both ours and of our adversaries. In your effort to make the story interesting, try not to make fun of people's suffering.

[1]   Four times Torah tells about teaching our children about the Exodus and the celebration of Passover: On Ex. 12:25-27; Ex. 13:14-16 and Deut. 6:20-25 we are instructed to tell the story of the Exodus in response to their questions. On Ex. 13: 5-8, we are instructed to tell them the story even though they don't ask (which the rabbis interpreted as the child who doesn't know how to ask.)

[2] Mishnah Pesahim 10:5.

[3]    Ex. 22:20, Ex. 23:9, Lev. 19:34, Deut. 10:19.

haggadah Section: -- Four Children
Source: Rogerio Zingerevitz Cukierman