From learning Japanese myself, I know that it is possible to cement the wrong thing into your mind. This has most frequently occurred in my case when learning two similar words on the same day. I still struggle with “kyouryuu” and “kyuuryou”, “salary payment” and “dinosaur”, respectively.

With the boys, Leo still struggles with questions about past events, often building sentences that use the past-tense of a verb: “Did you got ice cream at the store?”, “Did you went to the park with Joji?”
I react as though the sentences are horribly wrong, acting confused, and in all likelihood not helping the situation, but I want to drive home the idea that it’s quite wrong despite conveying what he means to say. Your language ability is how people will perceive you. You could be a brilliant surgeon, but if you talk like a caveman you may make people question your skills.

Joji recently worked past his phase of saying “Ya dis ya dis” where the first “ya dis” rises in intonation and the second “ya dis” drops down like a statement. I think it was his way of saying “what is this?” but it would also be used as “look at this” and rarely “tis a fine day”.

With past issues, they usually just disappeared one day when a “switch” was flipped in the brain. There haven’t really been situations were there were mixes of correct grammar or words with incorrect grammar or words. Leo said “contricity” for “electricity” for months…. until he didn’t.

Brains are interesting, and brains are weird.