Sentence:  the children were nothing like inert: a large population of junior <WSD>mudlarks</WSD>, so long unwashed that you could hardly make them out, climbed among the ruins, cheerfully playing the games that all children play – pushing wheels with sticks, flipping rusty lids and bottle caps in makeshift tiddlywinks. 
Meaning of the word marked with <WSD> tags:  A child who plays in the mud; a child that spends most of its time in the streets, a street urchin. (from 19th c.)