Uriah is my line, so I've gathered quite a bit of info.I don't think there is an unidentified child in Uriah's 1830 household to account for Hannah.
1830 Missouri Census - Salt River Twp, Ralls County (M19 #73), page 369 Uriah H. Hinch2 fwm 5-10 [Samuel, unk], 1 fwm 15-20 [John M.], 1 fwm 30-40 [Uriah], 2 fwf < 5 [Mary, unk], 1 fwf 5-10 [Charity], 1 fwf 10-15 [Louisa], 1 fwf 30-40 [Elizabeth]
And, yes, you are right that Uriah's will is written after Hannah's death.
Hinch, Uriah H., - will dated 18 Jan 1855.Wife, Elizabeth Hinch, the 80 acres of land on which we now reside and personal property, and after her death the remainder of the estate is to be equally divided among my three unmarried children, namely, Mary Pottorff, Asaph H. Hinch & Robert G. C. Hinch.One dollar each to my five children that are married, namely, Mariah Love?(Low?), John M. Hinch, Louisa H. McLain, Samuel Hinch & Charity H. Pullum...heretofore given.Forty acres to son, Robert G. C. Hinch (description). Exr. not named.Wit: R. M. Canterbury, J. C. Canterbury & Abraham Clements. Rec 7 Aug 1855. (161-162)
I have a lot more info.Feel free to contact me directly.