Without a doubt
No, there is no sharing allowed if you use the All Day Dine.
I don't know how they police it either but suffice to say it would be suspicious when you activate 1 kids plan & 2 adult plans and there is clearly another kid with you. And when you go through the line with 2 kids & 1 kids meal.
When are you going? If after mid-late Nov, SW has had Black Friday deals on the All Day Dining for the past several years, usually buy 1 get 1 half price.