There are a number of children who will all be around age 6 going into Season Five.
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Rebel Alley's Son[]
Ann Veal's Son[]
Baby Veal fathered by Tony Wonder
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Mark Cherry fan's granddaughter[]
Possibly the same person as one of the children below.
Maggie Lizer's Child[]
After receiving a positive pregnancy test this child of Michael Bluth is not referenced again.
Kitty Sanchez's child (speculative)[]
The one she would have had after stealing 250ccs of George Bluth. She only appeared sparsely after this season two episode making her having a child unmentioned on the show unlikely but not impossible.