Skeptics point out that differences in size were used to indicate differences in importance, power, or status: that’s why the pharaohs and the kings are shown significantly larger than those around them. Here's a pretty simple explanation from this website:
"The stratified sizes of god and human, king and subject, tomb owner and servant, parent and child or husband and wife are usually symbolic of relative status and power within Egyptian compositions. This is particularly clear in scenes recorded on temple walls and in other settings which show the Egyptian king at a much larger scale than his enemies, heightening the hierarchical effect of the representation by emphasizing the helplessness of the enemy and the king's superhuman stature."
Well, sure, that makes total sense. But it's also far too boring. We want giants, and we want them now. Even better if they're also aliens.
So let's ignore the pesky "symbolism" aspect for now and keep insisting that the size differences in the artwork were really meant to be taken literally. It turns out we still have a problem: the physical remains of many of those individuals depicted as "giants" are not giant at all. Because we're looking at depictions of known individuals, we can in some cases examine the actual remains of those individuals and see if they're gigantic (they're not). So if the differences in the sizes of the individuals in these pictures are to be take literally, we’re going to have to come up with a different explanation. I think I’ve figured it out: the rulers were normal-sized, but everyone else back then was super small.
I’ll give you the example of Rameses II. I think you'll agree that this explanation is just as plausible as giants.
Ramesses II (1303-1213 BC) is regarded as one of the most powerful pharaohs of ancient Egypt. Among his many exploits, he led military campaigns into Nubia and the Levant to expand Egypt’s control and secure its borders. Perhaps his most famous adventure was the clash with the Hittite Empire at the Battle of Kadesh (1274 BC), billed as the largest chariot battle ever fought.
Unfortunately for the giant enthusiasts, Ramesses was about 5'7" rather than 30' (or even 12' tall). We don't have to guess - we can just get out a tape measure.
That's a bummer for the giant enthusiasts, but great news for the super small people enthusiasts. Because if Ramesses was about 6' (we can round up - he was a pharaoh, after all), everyone around him appears to have been less than 3' tall. If we disregard the possibility that any attempt was made to depict distance in the mural shown above, we may even conclude that there are some 1' tall people shown in that artwork.
The really good researchers out there will be able to find other examples of artwork depicting normal-sized pharaohs and tiny people. Like his son, Seti I was about 5'7". The 1834 volume A History of Egyptian Mummies (published before Darwin and before the Smithsonian, notice) didn't list any mummies taller than 5'6".
I'm sure there is more to be considered here, but I think my super small people theory is looking pretty good. Unless, of course, we want to go back to the boring idea that artistic traditions include regularities for communicating ideas, and relative size was used in ancient Egypt to communicate relative status or power. I know it's boring, but is it really that crazy?