My oldest went through a period when he was young doing that, I actually think he picked it up from sesame street, but it's definitely one of those cool quirks of kids on the spectrum that us parents don't have to try to stop :)

Hun, my son is 12, he still does it. I never did figure out why. But hey just think, you won't have issues when he gets into higher grade in school & they have spelling tests!

Yea, when ever he wants something he spells out mommy. I don't always catch it the first time as I'm not expecting it, so he will repeat it. If he can spell the word then he will instead of saying it.