Passover is an 8-day observance commemorating the freedom and exodus of the Israelites (Jewish slaves) from Egypt. The Pharaoh's name is not recorded in the Bible, though many historians have suggested Ramses II.
The plague of the firstborn is a difficult one for young children to understand. The idea of all the baby boys being killed by an angel of God is even hard for adults to comprehend. You know your students. Give them as much as they can handle. The idea here is to set the foundation for an understanding of the Passover feast throughout the rest of the Bible.
There are several reinforcement activities that are centered on the Israelites leaving in a hurry and the unleavened bread. These activities are especially good for younger children that would not understand the plague of the firstborn.
The plague of the firstborn is the final straw for Pharaoh. He finally gives permission for the Israelites to leave Egypt. The Israelites are told to put blood from a lamb over their doorposts. God will pass over the houses marked with the blood. The Israelites had to leave Egypt in such a hurry that their bread did not have time to rise. This is why they celebrate the Passover feast with unleavened bread (without yeast). Matzah is commonly used as a staple during Passover. Traditionally, matzah is prepared quickly (often within about 18 minutes) to prevent rising. This is, again, representative of the Israelites leaving Egypt in a hurry.
Be sure to point out that the blood was to be from a lamb. Passover is a foreshadowing symbol of what Jesus did on the cross. That is why he is called the "Lamb of God".
Reference other times in the Bible when the Passover feast is celebrated. Luke 2:41-52, Jesus' family was in Jerusalem to celebrate the Passover feast when they realized he was not with them on the way home. They found Jesus in the temple. He was thought to be about 12, at this point; John 12:12-19, Jesus was going to Jerusalem to celebrate Passover during the triumphal entry. He spent the Passover with his disciples. This is where he washed the disciples' feet and taught them to serve others, just prior to his arrest.