Maybe we’re talking about the same thing differently then. When you say “square root function,” are you talking about the calculator function or the operation in general? Because while I think the positive solution to a sq root is the thing people think about first, you can’t discount the negative solution. I can’t quite recall what it got used for most during my math time (I want to say factoring), but there were problems we had that didn’t come out right if you used only the positive solution to the sq root. And it was definitely just using “square root;” there wasn’t another symbol or operation that meant “square root including negative solutions.”
What color were the sleeves of Napoleon’s green vest?*
I don’t know why, but mom always used Napoleon for these sort of questions.
I could use a collection of tricky trivia, more than ordinary brain teasers. My repertoire at the moment is limited to “10 Downing Street, London, is the official residence of what member of the British Cabinet?”, “Where was the Battle of Bunker Hill fought?”, and “In the stories of Sindbad the Sailor (sometimes “Seaman”), what was the profession of the title character?”
Of course, the answers are not the obvious ones.
What’s red and smells like blue paint?Red paint.
Or you tell the question the right way: a ship is tied to a quay with a line (which hangs with slack if you are in a port with tide, anyway), and so when the ship rises, the line gives in.
That’s a big pond.
Damn, I love this place.
Great for kids:
A man is trapped.
To have a chance at escape, he has to choose between three rooms.
The first is full of raging fires, the second is full of assassins with loaded guns, and the third is full of lions that haven’t eaten in a year.
Which room is safest for him?
The lions. They starved to death, right? 
Here’s a visual one. How many passes do the player in white make in this video?
And did you notice the guy in the gorilla suit?
A man and his son are in a car accident. The boy is badly injured, and the father rushers him to the hospital. At the hospital, the surgeon walks into the operating room, gasps in shock, and says “I can’t operate on this boy - he’s my son!”
How is this possible?
The surgeon is the boy’s mother.
I’ve read this one here at the SDMB, probably too tricky for young kids.
Which weighs more, an ounce of gold, or an ounce of feathers?
An ounce of gold. Gold is measured in troy ounces which are 31.1 grams; feathers would be measured in avoirdupois (“standard”) ounces which are 28.3 grams.
followed by: Which weighs more, a pound of gold, or a pound of feathers?
A pound of feathers. The troy pound has only 12 troy ounces, equal to 373 grams. The avoirdupois (“standard”) pound has 16 ounces, equal to 453.6 grams.
The First Lord of the Treasury is the Cabinet position the resident of 10 Downing St has, right? I have a recollection that I’ve been told that the Battle of Bunker Hill was actually fought on Breed’s Hill.
(The stories referred to by the third I’m not familiar with.)
However, none of those are riddles in which the answers are easy but require sideways thinking to realize. They require knowledge about world traditions, history, and literature that are not contained in the question and not easily inferred.
I walked 100 feet north, 100 feet east, then 100 feet south and realized I was where I started. Where am I?
The South Pole
Gesundheit.
Pull my finger.
Ok, it’s not a riddle, but it will amuse a ten year old.
Not necessarily.[spoiler]If you start about 130 feet from the North Pole, you can walk 100 feet north, 100 feet east (making one full circle around the Pole), and 100 feet south, and wind up back where you started.
Other answers are possible, too.[/spoiler]
No, there are such things as true white horses that are not just light greys or albinos. Search wiki for “true white horse”. I can’t link to it because I’m on mobile.
I recently read the thing about white horses are actually grey and asked a friend who’s into horses.
There is a genuine ambiguity in what one might mean by “the square root function”. One might mean a single-valued function from semipositive numbers to semipositive numbers; or one might mean a doubly-valued function from semipositive numbers to signed numbers; or one might mean a doubly-valued function from complex numbers to complex numbers; or one might mean a singly-valued function from complex numbers with a chosen logarithm to complex numbers with a chosen logarithm; or one might mean a multiply-valued partial function from an arbitrary multiplicative monoid to itself; or other things besides.
It’s not necessarily wrong to adopt any of these interpretations of the words “the square root of”, without further disambiguation.
None, it’s a hole, though I think the question makes more sense if you specify three dimensions.
You just moved to a new area. The red man lives in the red house, the blue man lives in the blue house, and the green man lives in the green house. Who lives in the white house?
The President. Doesn’t work as well in text because technically White House should be capitalized, but feh.
The red house is made of red bricks, the blue house is made of blue bricks and the black house is made of black bricks. What color bricks does a green house have?
It’s made of glass, not bricks, it’s a greenhouse. Another one that’s better out loud.
Shouldn’t the answer, currently, be The black man? 