Quarks

Daughter #2 much taken with the idea of quarks. She's made her own set of quarks which she carries around everywhere.

(There are two up quarks, because you need two ups and a down to make a proton.)

She asked me, "what is the smallest thing?" A quark was the smallest thing I knew. So then we looked up quarks on Wikipedia. Neither of us really understood the theory, but she liked the whimsical names. Anthropomorphism ensued.