An alternative title to this post might be: When do you use your child’s full name?
For my daughter, her name is typically said in soft, sing-songy way, so if she’s being naughty I usually just say her first name in a sharp, mom-voice. Something like, “EYE-laaaah!” With big emphasis on the first syllable. I sometimes say “EYElah Hooope” but usually the first name does the trick.
My son’s first name being 1 syllable, his middle name gets brought out quite often when he’s naughty. [name_m]Grant[/name_m] [name_m]William[/name_m] rolls off the tongue, especially when I’m trying to stop him from climbing the [name_u]Christmas[/name_u] tree, for example 
He was such a mild mannered baby and toddler, I remember the first time I said, “[name_m]GRANT[/name_m] [name_m]WILLIAM[/name_m]!” in a angry way and had to stop and think for a minute about what his middle name was because we so rarely used it, haha!
For #3 I’m leaning towards [name_m]Weston[/name_m]/[name_m]Wesley[/name_m] [name_u]Emmett[/name_u], but worry a bit that it’s too much of a mouthful. I’m wondering though how often would I say the full name. His nn would be [name_m]Wes[/name_m], so using his full first name in my famous mom voice would probably be pretty effective, without having to use the first and middle. Does that make sense?
I use their full names (first, middle, last) when I mean business. The tone I use has a lot to do with it, too.
First and middle with lots of 'tude.
I have some double-barreled to begin with, so for them I use both names all the time.
For the other ones, I use both names together around the house affectionately, in the same type of way I’d use a nickname or cute pet-name. I want them to feel ownership of their entire names.
I don’t reference the full name out of frustration though.
I have just always used his first name with an authoritative voice when I meant business. To little children I call it the “I mean it voice”. Now that he is a teen I seem to use it more than I did when he was younger. He is a very good kid though. I can see more and more how he will be as an adult. When my son was little we used to call him by his first and middle name, so the whole name was always used out of love.
[name_f]May[/name_f] I just say I adore your children’s names! I love [name_m]Wesley[/name_m] [name_u]Emmett[/name_u]. [name_m]Trust[/name_m] me…I think [name_m]WESLEY[/name_m] would get the angry point across 
I just use fn and mn if the kiddos I watch are in trouble. I do have one that I call Bug, though, or [name_u]Taylor[/name_u] Bug (her name is [name_u]Taylor[/name_u]). When I’m getting frustrated with her I just call her [name_u]Taylor[/name_u], if it continues her fn and mn.