Just out of curiosity, if your older child has already shown a preference for which hand they'll be using (left-handed or right-handed), did you notice when they were younger, whether or not they always shoved that fist in their mouth?
DD ALWAYS shoves her right fist in her mouth, and uses that hand to bring my fingers into her mouth, so I wonder if she'll be right-handed (DH's right handed, I'm left-handed... it's also interesting, cuz dad and I are left-handed, and mom and my brother are right-handed, and I take after my dad, and B takes after my mom....)