(This is not part of the Seder but explains the reasons for the specific plagues.)
"On that same night I will pass through Egypt and strike down every firstborn--both men and animals--and I will bring judgment on all the gods of Egypt. I am the Lord!" (Exodus 12:12)
1 - BLOOD
The first plague was blood (dahm) - Exodus 7.14-24. This was an attack on Hapi, the father of the gods, who was “god” of the Nile, the one who brings water to all Egypt for life. He was responsible for watering the meadows and bringing the dew. But most importantly he brought fertile inundation, the rising of the Nile. As a fertility god, he is associated with Osiris.
The Nile was considered the link from this life to the next. The Nile was considered the blood of Osiris. The priests of Egypt abhorred blood, yet they cruelly sported with blood of the captive Israelites whose children they caused to be cast into the Nile. The Egyptians worshipped the river. Other deities connected with the Nile are Amon, and Khnum who was the guardian of the Nile.
2 - FROGS
The second plague was frogs (tz’fahr’day-a) - Exodus 8.1-15. This was an attack on Heka (Heqt) the toad goddess, wife of Knepfh (Khnum) who was “goddess” of the land. Also, Heka was the goddess of the resurrection and procreative power. Frogs were consecrated to Osiris and were the symbol of inspiration. Frogs and toads were very sacred to the Egyptians. Killed a frog, even unintentionally, was punishable by death.
Something you may want ask the kids: The Bible says the plagues were a punishment and there were frogs everywhere. Where did the frogs "go to the bathroom?"
3 - GNATS
The third plague was gnats (kin-nim) - Exodus 8.16-19. This was an attack on Geb, "the great cackler," god of the earth or vegetation, father of Osiris and husband of Nut.
The fourth plague was flies (a-rov) - Exodus 8.20-32. The word a-rov can mean either flies or wild beasts and both translations are used. This was an attack on Khepfi, the scarab beetle, god of insects. The scarab was an emblem of Re (Ra), the sun god.
5 - LIVESTOCK DISEASE
The fifth plague was livestock (de-ver) - Exodus 9.1-7. This was an attack on Apis, the bull god. His female counterpart was Hathor, the cow goddess. Their place of worship was at On (Heliopolis). The Egyptians held many beasts in idolatrous veneration. The lion, wolf, dog, cat, ape, and goat were very sacred to them, but especially the ox, heifer, and ram (Khnum). The soul of their god Osiris was believed to reside in the body of the bull, Apis. Mnevis, the bull god, was THE symbol of fertility.
6 - SKIN BOILS
The sixth plague was skin boils (sh’chir) - Exodus 9.8-12. This was an attack on Thoth (Imhotep), god of medicine and intelligence/wisdom. The Egyptians had several medical deities. They performed human sacrifices on special occasions, burning people alive on a high altar and casting their ashes into the air, so that a blessing might descend upon the people with every scattered ash. Moses took ashes from the furnace and cast them into the air. The ashes were scattered by the wind, descending upon all the priests, people, and beasts causing boils, thus shaming the god Thoth.
7 - HAIL
The seventh plague was hail (ba-rad) - Exodus 9.13-35. This was an attack on Nut, who was the sky “goddess,” for this was harvest time, the time of plenty. Like her husband Geb, HaShem attacked and destroyed the crops. She was the mother of Osiris. Also, this was an attack on Isis, goddess of life, and Seth, protector of crops.
It helps to understand the Egyptian climate. Buildings were made of mud bricks consisting of dried mud and straw. Even today many Egyptian homes have rooms with no roof because it simply doesn't rain in Egypt.
8 - LOCUSTS
The eighth plague was locust (ar-beh) - Exodus 10.1-20. This was an attack on Anubis, god of the fields, especially cemeteries. This plague finishes up the damage done by the hail. They devoured every herb of the land and fruit of the trees. Also, this plague was an attack on Isis, protector against locust, and Seth, protector of crops.
9 - DARKNESS
The ninth plague was darkness (cho-shekh) - Exodus 10.21-29. This was an attack on Ra or Amon-Re, the sun god. Darkness was considered a creation of Seth, evil principle destroyer of Osiris. It seemed Re (Ra), the sun god, was dead; and Seth had killed him. This plague was so terrible that the darkness could be felt! At the same time that the Egyptians had darkness, the Israelites had light. Ra was believed to be the physical father of all Pharaohs. Pharaoh was the king of all gods.
The tenth plague was death of the first-born (mak-kat b’kho-rot) - Exodus 11,12. This was an attack on Pharaoh, who was the "god-king." Pharaoh was considered a god, as well as his first-born son who would succeed him on the throne. First-born people and animals were often worshipped. Pharaoh was considered an incarnation of Ra, the sun god, and Osiris, the giver of life. Because Pharaoh’s son was considered a god, a god of Egypt actually died.
This plague HaShem used to humble Egypt for the cruel ways that she had treated His people. Egypt had enslaved Israel and murdered her male children, but HaShem, struck back with an awful vengeance. His righteous anger was made known upon every house that was not covered with the blood. When HaShem saw the blood, he passed over.