From your question:
As per the kid, 2/4 is more than 1/2 since in first case the boy gets 2 candies out of 4 and in second case he gets 1 candy out of the 2.
Getting 2 candies out of 4 is because 4/2 = 2. But 2/4 means 2 cookies and 4 hungry little kids. 1/2 is 1 cookie and 2 hungry little kids. Ask your kid what they prefer now.
For kids, I always use the pie (or pizza) example, cutting it into pieces. This way it is very visual and easy to understand that 1/2 is the same as 2/4.
With the fraction program you can do any "cutting" of a circle interactively. Just set 1/2 and then 2/4. (Disclaimer: I am the developer of the website, it is in German.)
Following an example how you can ...
I once read a suggestion to explain the difference between local and global maxima by using the example of Mount Everest (global maximum of the height function) and K2 (local maximum). I consider this a bad example because it gives two erroneous impressions: (1) local maxima almost achieve the global maximum value (because K2 is almost as high as Everest) ...
Do it in yearly steps (also allows you to see the yearly financials, a feature, not a bug). Don't just plug into some compounding formula. If you do it in Excel that is best.
I could tell you exactly how to set up the (very simple) spreadsheet. But it's better if you try first. Report back if you still have problems, but after giving it a shot.