In a nutshell:
Below is a link in which to download a little booklet I made for my kids, that might be of interest to yours as well. ,
… The situation:
An exceptionally mathematically-gifted child asks his mother: "What's one thousand plus one thousand?" Mom answers: "What's one frog plus one frog?" – "Two frogs", says the boy immediately. "So what's one thousand plus one thousand?" asks again Mom. "I don't know", the boy shrugs.
Mom is alarmed: she is certain that this is a first expression of a mathematical anxiety, which must be destroyed before it gets a chance to settle for good. How else can one explain seeing (large) numbers as unique objects, different from any other addable objects?...
Since the oral explanation was forgotten after a while (and the original question sprung once again), Mom decided to write it down (and add pictures). The important principle shown is that addition is always addition, no matter what objects we add: tangible objects, numbers (or other abstract objects), and even concepts which we don't understand their meaning , or which don't exist in reality.
Here is an adobe acrobat (pdf) file in a regular printing mode (every sheet contains one page), and a "challenging" file, in the shape of a booklet (with two pages in every sheet, which requires paying attention when folding and putting the pages together, but allows for forming a booklet).
Happy new year! ,