My 7 year old DD uses ‘what’ in place of ‘that’ when speaking and in her writing despite my constant correction! Neither myself, nor any of her family, make the same error and I don’t think she has heard it from her school because we aren’t from an area with any strong regional accent.
An example would be “this is a picture what I drew” instead of “this is a picture that I drew”. I can’t think where she picked up this way of speaking. What once may have been endearing (like the way toddlers’ mispronounce words), is starting to drive me up the wall. Has anyone had this before with their children and did it continue as they grew?
I think she must of been cockney in a past life!