Sharing this video simply because it makes the word nerd in me chortle with glee:

"" (Watch on YouTube)

Readers' Digest version:

English has a lot of odd plurals; before the viking invasion, it had a lot more. But the vikings came over as grown-ups, had too much trouble keeping all the plurals straight, and so replaced most of the weird plurals with "Stick an 'S' on the end." They married the locals and simplified English became the language of Home, and stuck. The oddballs that remained, such as: Men, Women, and Children, did so because they were used so often that they were too hard to shake.

A few of the odd plurals that are no more:

One Book, Two Beek
One Lamb, Two Lambru (and Two Breadru, and Two Eggru)
One Goat, Two Gat (and Two Ack)

And, after all that, how can I not include this video?

"" (Watch on YouTube)