According to the Catholic Church, what was the point of all the plagues? Did God really have to do all those plagues in order to get Moses' people free? Did each plague have a particular purpose? I heard about a documentary or hypothesis that only first or first few plagues were intended and then the remaining plagues, except the last one, just occurred naturally.

Even if we grant that all but the last plague were purposeful or natural, what was the point of killing innocent children, particularly the Pharaoh's son? Why not kill the Pharaoh and then have the son or regent rule and then have the next ruler of Egypt set Moses' people free? Why not send a bunch of angels to threaten the Pharaoh into releasing the Israelites or into offering fair wages?

I doubt this is relevant to the problem of evil as God specifically intervenes in human affairs in Egypt. Why all the violence though? It seems to make sense that an omnipotent, omniscient, all-good being who would intervene in human affairs would want to do so with little bloodshed unless there's a specific lesson that the being wants to impart on the Egyptians or Israelites or something of the sort. Maybe the Israelites wouldn't have appreciated God's efforts as much if it was that simple?

Also, I seem to recall from high school something about wanting to convert the Egyptians.

What does the Catholic Church say about this?
The ten plagues corresponded to ten of the major Gods of the Egyptians. The God of the Hebrews wasn't trying to convert anyone, but assert himself as the God above all other gods.

1) God of the Nile, Osiris &amp; Hapi? Your river is blood.

2) Frog-Goddess of Fertility, Heka? You get frogs, you get frogs,
   everybody gets frogs.

3 &amp; 4) Geb, the god of earth, and Khephi with the head of a fly? Your
   soil is now lice, with a super size side of flies.

5) Bull god Apis? Livestock struck down. (EDIT: Also, Hathor)

6) Thoth, the god of medicine and cleanliness? Boils everywhere.

7) Nut the sky goddes and Shu the wind god? Storms of hail &amp; fire.

8) Seth, the god of crops and Isis, protector of the fields? Why don't
   you have some locusts.

9) Sun god Ra? Darkness.

10) Your Pharoah sells himself as a god, and his son will be a god after
   him? Kill the firstborn... but not just his, but everyone's
   firstborn.

(The Apostolic Vicariate of Southern Arabia holyspiritinteractive.net/youth/biblegeek/35.asp)

The God of the Hebrews was impacting the whole of the Egyptian society with those plagues, both physically and spiritually. At the same time, he was showing favor to his chosen people, sparing the people from all of the plagues, especially "Passing over" them on the tenth plague. The God of the Hebrews wanted to make a lasting impact on not only the people of Egypt, but everywhere else too - Remember, the reason Jericho wound themselves up tight is because they heard of what happened in Egypt. Following that, the reason the people of Gibeon presented themselves as travelers from far, far away is because of what God did in Jericho. 

In our minds, the God of the Hebrews can kinda seem overkill. And it isn't just in Exodus, you also see it in:


Elijah's highly-successful barbecue in 1st Kings 18, where the
prohpet not only placed the offering, but soaked it to the point of
filling up the moat dug around the alter... and then YHWH cooks the
entire thing, to the point of even boiling the water in the trench.
When He institutes the cleansing of the land of Canaan, He says to
destroy everything of the inhabitants, not only the idols, but the
livestock and treasure as well... and when Achan defies this order in
Joshua 7, not only does he get stoned and burned, but also "his sons
and daughters, his cattle, donkeys and sheep, his tent and all that
he had".
Jesus doesn't politely show out the monylenders, rather making "a
scourge of cords, and drove them all out of the temple, with the
sheep and the oxen; and He poured out the coins of the money changers
and overturned their tables" in John 2.


And many, many various other places in Scripture. The church response to all this is that God is passionate about his own glory, and will shake anything that stands in the way to the foundations to crush it with his heel, from Babel in Genesis to the Beast in Revelation.