Yes, I now think I realize why Poles find Czech childlike
AFAICT (thinking about this for a long time) it's three things
intonation (esp Prague) - long vowels in unaccented syllables give Czech a kind of sing song quality (there's more but that's enough for now)
diminutives - Czech frequently uses something like (i)cz(e)k which is a single diminutive but sounds to Poles like a double diminutive so psíček sounds like pieseczek rather than its real equivalent - piesek
Czech neologisms - lots of times the result of normal Czech word building ends up sounding funny to Poles so (to use a famous example) the Czech word for theater (divadlo) sounds like dziwadło (weirdo) to Poles (the czech root is about watching - I'm not sure if it's related to the root in dziwny or not...)
the cumulative effect of all these (and maybe a couple of other factors) mean that Czech sounds childlike and funny to Poles - Polish sounds funny to Czechs (absurdly wordy among other things) but not especially childlike.
