Childishly

She talked childishly.

You may not behave so childishly.

You're childishly naive.

The old corpuscular theory of light, which now seems so childishly incomplete to us, was adequate, none the less, for satisfactorily explaining the phenomena of reflection and refraction, and the finest telescopes have been built with its help.

I knew, of course, it was but an innocent game on her part, a bit of backfisch foolery in imitation of some simulacrum of fake romance, and since (as the psychotherapist, as well as the rapist, will tell you) the limits and rules of such girlish games are fluid, or at least too childishly subtle for the senior partner to grasp—I was dreadfully afraid I might go too far and cause her to start back in revulsion and terror.