Created databases and inserted data on MySQL slaves in Master-Slave replication - how to fix?
You say:


  databases have been created on the slaves and filled with data. 


The easiest way of correcting this is to take a mysqldump of the specific databases on the slave, drop the database on the slave, and import the dumpfile onto the master. The slaves will then replicate the data. 

This of course gets trickier if it is not whole databases or even tables (but specific rows inside a table).