twilight just before sunrise
曈 centers on the dim, transitional light just before dawn: twilight just before sunrise.
曈 combines 日 (sun) with 童, which likely contributes the sound トウ. The character expresses the dim light of early dawn.
The sun 日 is still low, and the right side 童 suggests a child-like faintness: the light is weak and dim, like twilight just before sunrise.
For トウ, imagine the faint glow of a toe just visible in the dim pre-dawn light: toe -> トウ, and the sun is barely peeking out.