well-known midwesterner

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.