ONE TRAIN MAY HIDE ANOTHER

Some AAVE speakers pluralize 'child' as 'childrens'. People get racist about this ("It's already plural!"), but 'children' actually comes from Middle English speakers doing the same thing: slapping their plural marker on word already pluralized by an extinct plural marker.

To oversimplify: in Old English, 'childer' ('ċildra') was the plural of 'child' ('ċild'). Middle English developed an '-en' plural marker, which we see in 'oxen'. Instead of updating to 'childen', people slapped their preferred '-en' onto the end of 'childer' - so now we have 'child-er-en'. AAVE carries on this tradition with 'child-er-en-s'.

"Pure" language is just impurity obscured by the passage of time.