To me, in order to believe that Casey was capable of killing her child because she was learning to speak is, I would have to believe in many other bizarre theories. I don't see someone killing their child because they're learning to speak. Isn't it expected that one day your child will talk? Why wouldn't she just not have the child, have an abortion, or kill the child before when it became clear that her child would one day learn to talk. Seriously, is it not common sense that your child will be talking one day?
And, what exactly was Casey trying to hide so much that she didn't want little Caylee tattling on her for? That she was out dating? That she didn't have a job? Come on! Casey lied to her parents about her pregnancy and I would think that's an even bigger lie then that she's not really working. And, she was stealing money left and right, I hope Casey would've realized that she wasn't that great about lying on the job thing. And the dating thing. If we believe Cindy truly gave her space so she could solidify a relationship with Jeffrey Hopkins, why would Casey kill her child so she could actually solidify a relationship with Tony? He didn't appear to be that bad of a guy, and it appeared like he liked Caylee. I'm sure Cindy would've accepted Tony if this didn't happen.
And, Casey took Caylee with her everywhere when her mom didn't babysit. And, her mom didn't babysit often enough for me to consider her a neglectful mother just trying to toss her daughter off on her parents. I've seen people like this with my own 2 eyes, and Casey didn't once appear to me as someone who thought her child was a burden. Yes, she made one comment that I know of calling her child a snot nose brat (or something like that), but one comment? She also made a comment to a friend about her daughter pooping in the potty.
To me, Casey would've been happy of the relationship Caylee had with Cindy. Keep in mind, Caylee didn't have other grandparents, other aunts and uncles, other family members in her life. Cindy was the grandmother, and that was that. Casey would've been grateful for her to be in Caylee's life. There was no other family there for Caylee, no other grandmom. I don't think Casey would get pissed and kill her child over some jealousy. Why not just take Caylee away from the family to 'show Cindy'?