Heh. My first exposure to Tezuka was Phoenix, which I then followed up with Buddha. I didn't get around to Astro Boy until this year, so for me it was his kid stuff that took some getting used to.
No major cognitive dissonance, exactly. Tezuka's round, cartoony style is a natural fit for all ages work. But the tone and pacing was so different. I was used to the much slower, more reflective pace of his grown-up stuff. It's not that his children's stuff is less thoughtful, but the thinking is shorter and quicker and interspersed with ROBOT FIGHTS!! It zips along. There was a teeny bit of mental whiplash.