complex conversation

is there a delicate way to discuss psychology with a 7 year old? i just tried...tough one though.  chesley and charsy were climbing on my oh so fabulous four legged walker. my walker has little side rails for lack of a better description. charsy climbed up to the top rails and chesley was trying to climb to the secondary side rails but her head was hitting charsy's crotch. (i am aware of frued's second stage of the psychosexual stages...the anal complex stage taking place around ages 1-2. i am aware chesley is very much into this bottom thing...and other peoples bottoms.) so i tried very gingerly to explain to charsy that we didn't want to encourage the behavior of chesley ramming her head into charsy's, or anyones, bottom. charsy thought it was hysterical and yes once funny but repeatedly...no. so the conversation included the word complex (not anal just complex) and charsy, 7, said "what's that" thus i explained how people could get a strange way of thinking about an act or an object that hinders them in some way potentially (look i was on the spot) to which charsy replied i don't know any of what you just said and hopped off the walker. i just gave a giggle of relief and finished my walk to the dishwasher.