Kids are incredibly distracting with their questions that disrupt your train of thought. I'm not talking about some profound question about the nature of the world around them but rather things like: who's your favorite Pokemon, your favorite land animal, who's more powerful Aang or Goku? It's not that I don't want to answer these questions but rather I've already answered them multiple times or the answer should be fairly obvious. They also tend to ask these questions at the most inopportune times like when you're running late.
This is on top of mundane considerations like did they bring their backpack? Drink enough water, visit the restroom, wash their hands, etc.
I also find that reading stories disrupt my normal focus or rather I should say they consume mental cycles that leave less cycles for other things like noticing whether I've rolled up my car windows. This happens even when I'm not actively thinking about what I've read. The recent XianXia translation explosion, and my access to an iPhone has affected me greatly since I've been following pretty much every translation. Of course it could just be the early onset of Alzheimer's.