If I gave you, let's say, a box- or package- and tried to tell you that it's 'Bottom' was Halfway Down... you would think me Mad(der).... BUT Your HEAD is at the 'Top', Your FEET are at the 'Bottom'.... and where IS your 'Bottom'? If you want to search someone 'Top To Bottom'.... you Start at the Head but do you them stop at their 'Bottom', or go on to their Feet?
If you went to the Doctor, for a 'check up', and complained of a Sore Bottom.... would (s)he look at your Feet? If you are all told to 'Put Your Bottoms, On That Seat' is the one STANDING on it wrong? (I just Love the, apparently true, story of the ' Notice', by the sinks, at the Local W.I..... Said Notice was Clearly 'Aimed' at those making the Tea however, it read "Please Do Not Put Hot BOTTOMS On This Counter".)
One 'Things', for sure.... when 'your Little One 'Needs' a Bottom Change'... (s)he doesn't have Dirty FEET!