Driving the 4 Year Old home from school, he sees a symbolic 'No U-Turn' Sign.
4 Year Old: "Look mom, that says no driving down"
Me: "Well it means no U-turns, but the U arrow does look like it is pointing down and the red circle with a slash means 'No' on the sign"
4 Year Old: "Yes, it means no driving down."
Me: "How about driving up, can we do that?"
4 Year Old: "Nooooooo! We are in a car, we would have to be in an airplane to go UP in the air.  Or a helicopter.  Or be birds.  Or be in a rocket ship.  Or a balloon with a string on it.... Or..."
The list went on for a few more flying examples.  The little man likes to make his point.  At least he is using concrete examples and data to back up his statements. 

6 Year Old Building objects with some interconnecting bath toys, makes a simulated 'metal detector'.
6 Year Old: "Mom, is there metal in metal detectors?"
Me: "Yes, there is some metal in the design"
6 Year Old: "But how can there be METAL in a METAL detector?!? Wouldn't it just keep sensing itself and beeping?"
Me: "Good question, no the detector only looks for metal in front of the sensing face of it."
6 Year Old: "Oh ok"  ***looks off into bathtub space, I know his mental wheels are turning***
6 Year Old: "Wouldn't it be cool to find a metal detector buried on the beach by using a metal detector, then they could sense each other!"
Me (smiling):  "Yes... that would be awesome!"

The 6 year old and I were playing with the Beyblades (neat design of spinning tops that kids can take apart and swap pieces to reconfigure, with a pull strip launcher), with the 'Beyblade Arena' (plastic arena for top 'battles' of who spins longest and bangs into the other knocking them down).
We decided to each launch 3 Beyblades at the same time (fun experiment in getting all 6 going at once).  So we made teams....
Me: "I will be team Blue Otter!"
6 Year Old: "I will be team Dancing Shark!"
Me:  "Who will win in a battle Blue Otter or Dancing Shark, we will see..."
6 Year Old: "Well actually mom, an otter and a shark would never meet to battle, they do not live in the same habitats.... one is in fresh water and the other salt water"
Me: (*smiling*) "You are technically correct"  "Let's assume in Beyblade land, Team Blue Otter and Team Dancing Shark can meet to battle it out"
6 Year Old: "Ok mom, let's go!"
Dancing Shark Won ....this time, but this Blue Otter momma will be practicing for our rematch.

Driving the kids home from school, the 6 year old, in a very serious voice says "Mommy, can I tell you something?"
Me: 'Of course, you can tell me anything' (I am mentally preparing myself for some incident at school, etc.)
6 Year Old: "Geckos can lick their eyeballs....They don't have eyelids, so they lick their eyes instead"
Me: 'Oh... awesome!'  The 4 year old, of course, then has to try this, I hear him from the back seat...
4 Year Old:  (in his frustrated voice) "I can't reach my eyeball with my tongue, my tongue is not long enough!!!"
A good lesson to me not to fret when the 6 year old 'needs to tell me something', I should not assume it is something serious or an incident from the day, eyeball licking is just as important a discussion in his world.

Over breakfast, I asked the boys "What is your favorite thing to build?"
4 Year Old:  A house, you take a square on bottom and then put some pieces on top to make a triangle roof (holding his hands together in a triangle to demo over his pancakes)
6 Year Old: A robot that moves!  You takes pieces of all shapes, and a motor and make it do stuff.
Me:  How do you power your robot?
6 Year Old: Solar power to charge the batteries... No not solar power, I will make FART powered batteries
*Both boys laughing close to the milk coming from their noses point*
Me: A fart powered battery, that would be one stinky robot! (I wonder if little girls find potty humor so funny, the number of fart and bathroom related jokes and ideas is my house is very high... but hey, if it makes them think about how to power a robot with an 'alternative' energy... fart batteries it is!)

I setup a magnetic marker board.  We make a  silly sentence out of the magnetic words, and one of the kids has to read the sentence and draw the image they picture in their head.  This is the 6 year olds: "The blue moon was going down in the green girl's dream".  Great imagery, descriptive diagraming, and reading practice all in one.

While my husband was on kid watching duty he found a new awesome math game for the 6 year old.  He told the 6 year old he will teach him 'computer math'... aka Binary.  Looks like the little man got the idea.  Like writing in a secret spy code.  I tried to make up another math game with the 6 year old after this, and he asked for the 'Computer Math' game instead... had quite an impact.