That's all the the vowels and 3 consonants!  Trent said one day he was trying to get him to go to sleep but he was too fussy, so Trent spent some time pointing out letters on a sign, and these ones stuck.

I'm floored.  I'm also feeling a little obsolete. When Trent learned all his letters, I was there, I was the one who taught them to him. Same with Myles, same with Rourke.  But Janney and Asher seem to be learning by osmosis!