See, this way we can spot them earlier. Way too many of them go on to live their dream—when they could have had their course adjusted at the beginning.
By this definition, Xolo wouldn't fit because the x in Xolo is somewhere between sh- and ch-. It's a Nahuatl word and many (if not all) Xs are sh-/ch-.
The Nahuatl word Xoloitzcuintle is something the vast majority of English-speaking Americans can’t read, let alone spell or pronounce correctly. So the more digestible word Xolo was adopted to identify Mexican hairless dogs (hard X, hard O, L, hard O).
When were talking about teaching kids the alphabet we need to train both individual and applied letters
This is only slightly related but I once met a young (USAmerican) adult who thought the stripy horse animal's name was pronounced zed-bra in British English and it was really hard to convince her otherwise. In her mind zebra was strongly connected to Z-bra, so of course if someone was to pronounce the letter "zed" it would turn into "zed-bra" and not just into "zeh-bra".
Xylophone: fun, colorful, easy for a kid to remember as a cute little instrument
Xenon: An inert gas used in... MRI scans, I think?
X-ray is probably the only other 'X' word with more real-world representation than xylophone, and as pointed out above, that's not quite representative of how the letter is used phonetically in the rest of the language.
By "real-world representation", I mean "how often the word is actually used in the real world." There are hundreds of trillions of neutrinos passing through you all the time, but I'd still think "nest" is a better word for kids.