I suspect there are some regional differences in the pronunciation, but to me (who lives in southern China) the following applies:
小孩(儿) - optional
一点(儿) - (in the sense of "a little bit") optional; (in the sense of "one o'clock") always without
一会儿 - mostly necessary, but understandable without
一块(儿) - (in the sense of "together") optional; (in the sense of "a piece (of)") always without
好玩(儿) - (in the sense of "enjoyable; fun") optional; (in the sense of "interesting; attractive because of its peculiarities") necessary
OK, I consulted the dictionary (《现代汉语词典》 if you wonder), and it totally shocked me.
小孩儿, 一点儿 (a little bit), 一会儿, 一块儿 (together), 好玩儿 all require 儿 in spoken language, but it is optional in written language.
I don't see anyone cling tenaciously to this prescription though.