How do I explain to my six year ols how two minuses makes a positive when I can't even explain it to my my high schooler?

I misspelled olds. I think the answer to the question is : they don't.

Erm... just explain that in division and multiplication (if this is what you're talking about) when the two signs are the same, they make a positive, and when the two signs are different, they make a negative.

+ + = +
- - = +
+ - = -
- + = -

That was the way it was explained to me.
I hope this is what you were looking for? :)

two minus make positive make sense in the operations with real numbers.
In addition and subtraction, minus a negative number means plus it's opposite, e.g. 5-(-3)=5+3
In division and multiplication two negative factors make a positive product. e.g. -5*-3=+15
hope these make sense.

well because adding a - is plusing a positive show them using a number line... that is easier ^^ if you know what I mean by that.

Are you talking about the product of two negative numbers? There's several ways you can go about internalizing the concept you speak of. One way is to just let them do it on a calculator. Eventually they'll observe that the calculator always returns positive answers. Another way is, if they understand that the product of a positive and a negative number is negative, such as 3(-2)= -6, then explain that making it (-3)(-2), thus introducing the second '-' sign, makes it the opposite and the opposite of -6 is 6.

You can explain to them that when the two dashes - - (minus signs) come together. The meet and bond together to form the two dashes that make a +.

- - bond to get +

Hard to explain in words but it was a handy little rule a teacher taught me that stuck. I need a pen and paper.

The two subtraction symbols when together interlock with one another one another to form a the plus sign. Imagine it as an illustration. Hope I make sense. If not I just sounds like a dribbling fool!

Oh well, won't be the first time.